Traced eastward, the section alters somewhat, is well exposed under the saddle on the west side of hill 4952, and has essentially the same thickness as the preceding section. On the west side of this easternmost hill of the Wolf Camp Hills, the mas- sive Gaptank is followed by 16 feet of cobbly beds, which are overlain by the lower brown layer with Syringopora 32 feet thick. This is succeeded by a shaly-cobbly slope representing an interval of 26 feet. The capping limestone of the Uddenites-bear- ing Shale Member is 15 feet thick, but the overlying shale has disappeared. Scacchinella appears in the cobbly beds and in the upper thick limestone (15 feet) overlying them.
The upper (15-foot) limestone forms the floor of this easternmost saddle and of the dip slope to the north on the west side of hill 4952, and it
FICURE 4.—South front of the Wolf Camp Hills showing the position of members and formations (G=:Gaptank Formation, G L = G r a y Limestone Member of P. B. King, GM—upper massive bed of Gaptank Formation, H = Hess Formation, SC=Scacchinella, U=Uddenites-bearing Shale Member of Gaptank Formation, ULrz upper limestone bed of Uddenites-bearing Shale Membei that contains Scacchinella; see Plate 2: figure 2) .
directly underlies the 135 feet thick knob that caps the hill. T h i s knob is the Gray Limestone of P. B.
King, here completely altered to dolomite. O n the slope forming the front of these two hills, 4950 and 4952, the upper Gaptank ledge undulates at dif- ferent levels, causing the Uddenites-bearing Shale Member to change i n thickness.
T h e northeast slope of hill 4952 also exhibits Uddenites-bearing Shale Member, b u t it is impos- sible to make a section on this slope because of the debris a n d float blocks covering the surface.
T h e upper limestone (bed C) of the section in hill 4950 appears to thicken. T h e brown bed in bed A also appears to thicken and blocks of it are a b u n d a n t on the slope.
Uddenites-KEARixG SHALE MEMBER NORTHEAST OF W O L F C A M P HILLS.—The u p p e r Gaptank is vari- able along the front slope of the foothills extend- ing northeast from the Wolf Camp Hills to the Fort Stockton-Marathon road (U. S. Highway 385).
A small irregularly conical hill with about 4,850 feet elevation (top contour) lies 1.5 miles northeast of the eastern end of the Wolf Camp Hills. Here a section of about 450 feet is exposed, b u t the few fossils collected do n o t warrant its correlation with the Uddenites-bearing Shale Member. T h e base of the section is dark biohermal limestone crumbling to cobbles. I t contains algae, the brachiopods Teguliferina and Hystriculina, and may be the same limestone as that underlying the Uddenites- bearing Shale Member i n the Wolf Camp Hills.
Above it comes a sequence of 155 feet of shale with thin layers of brown limestone containing eugonophylloid algae. T h e shale is capped by 38 feet of sandstone a n d limy sandstone, followed by a partly covered sequence with shale and lime- stone in the float for 45 feet. T h e section is capped by 95 feet of massive and granular limestone form- ing a high bluff. P. B. King (1931:145, section 26) places this limestone at the base of the over- lying Hess, b u t it contains Gaptank fusulinids and may represent a thickened extension of the upper limestone of the Uddenites-bearing Shale Member of the east end of the Wolf Camp Hills. T h e Hess conglomerate is n o t exposed on this hill, and the thick upper Gaptank limestone is succeeded by red shale of the Hess Formation ( = L e n o x Hills equivalent of Ross).
Goniatites of the Uddenites-bearing Shale Mem- ber were found i n the slopes of a chain of foot- hills beginning two miles northeast of the east end of the Wolf Camp Hills. T h r e e n u m b e r e d crests identify these foothills from southwest to northeast: 4815, 4752, and 4762. T h e sections mea- sured under these hills are dissimilar, b u t all con- tain a lower shale, usually a thick sandstone, and a thick, capping, bluff-making limestone that is overlain by the basal conglomerate of t h e Hess Formation ( = L e n o x Hills of Ross) (Plate 19:
figure 3).
A small knob at the base of hill 4815 is capped by a thick biohermal ledge of G a p t a n k limestone that holds u p the crest of the knob. O n top of this lies shale with large tetracorals near the base. This is followed by shale with thin layers of brown lime- stone and sandstone that are succeeded by a thick sandstone capped by the limestone forming the prominent cliff at the top of t h e hill. T h i s lime- stone can be traced for some distance along the mountain front. It is n o t the Gray Limestone of P. B. King (as King originally supposed), b u t prob- ably it is the u p p e r limestone capping the Ud- denites-bearing Shale Member just below the Gray limestone at the east end of the Wolf C a m p Hills.
T h i s correlation is based on the fact that it con- tains Triticites primarius Merchant a n d Keroher, which also is found beneath the Gray Limestone in the Wolf Camp Hills. King (P. B., 1942:649) also came to this conclusion when he stated: " T h u s the gray limestones mapped as Wolfcamp immedi- ately west of Gap T a n k now appear to belong to the Gaptank formation. . . ."
At the hill capped by summit 4752, the section is thicker and the massive beds of sandstone are miss- ing. These thick sandstones are evidently lenticular, because they appear at different levels a n d cannot be traced for long distances. At hill 4752 a thick bed of shale at the base of the section contains two beds of brown limestone 60 feet apart that yield goniatites including Uddenites. T h e upper bed is USNM 70lr ( = bed 13 of P. B. King, 1942:
55, section 27) and the lower one is reported by P. B. King (1931:55, bed 9, section 27). T h e top of the hill is capped by a thick layer of limestone, a thickened extension of that appearing in the hill 4815 to the west. T h e capping limestone is over-
lain by conglomerate a n d red shale of the over- lying Hess Formation ( = Lenox Hills of Ross).
In the easternmost hill (4762) a somewhat shorter section is revealed. Here the lower slopes are cov- ered, b u t , where the hill steepens, shale containing thin beds of brown limestone a n d sandstone mea- sure 105 feet. T h i s is followed by 45 feet of sand- stone, a n d this in t u r n by more than 100 feet of gray a n d white limestone, the upper, harder white part standing o u t as a prominent bluff. T h i s is undoubtedly the same limestone that forms the capping ledge of the foothills to the west and prob- ably to the east, except in the Wolf Camp Hills, where the Gray Limestone is the capping ledge.
T h e Hess conglomerate appears on the northside of a small ravine that divides this hill from the main m o u n t a i n front. T h e Uddenites fauna was not identified with certainty to the east, and fossils are so few a n d difficult to find in the vicinity of Stockton G a p that the Uddenites-bearing Shale Member was not identified at this place.
O T H E R GAPTANK LOCALITIES.—The large area of Gaptank west of M a r a t h o n was not studied exten- sively, b u t two localities south of the Arnold Ranch are of interest. A n important place for brachiopods is exactly 1.25 miles due south of the Arnold Ranch.
T h i s place was discovered by accident in our effort to find the ammonite bed from which Prouddenites and Uddenites were taken. O n the P. B. King m a p
(1938: pi. 16), the ammonite bed is located 1.25 miles south of the Arnold Ranch. It actually oc- curs 1.95 miles south of the Arnold Ranch ( = King locality C, not B — U S N M 700g of Cooper) and is located incorrectly on the Geological Survey map. T h e ammonite locality appears correctly on the m a p by P. B. a n d R. E. King accompanying the Geology of the Glass Mountains (P. B. King, 1931).
T h e locality 1.25 miles south of the Arnold R a n c h ( = locality B of P. B. King, 1938: pi. 16) like the ammonite locality farther south, contains a large, solid biohermal mass of limestone. T h i s appears in a shale enclosing cobbly limestone beds.
T h a t the mass is a bioherm is evident because it is n o t bedded, contains much finely laminated limestone, suggesting algae, thin-cupped colonial corals (Amplexocarinia) in abundance, and scat- tered brachiopods. T h e mass is about 20 feet long and 3 to 4 feet high. T h e rock is massive a n d
extremely hard as it has not been appreciably weathered. T h i s locality is noteworthy because it is a Pennsylvanian bioherm comparable to many of those in the Uddenites-bearing Shale Member.
It is also noteworthy because of the prenuncial Permian types of brachiopods it contains. These are Limbella a n d Scacchinella, the latter a primi- tive form with little or n o vesicular tissue in the apex. T h e one specimen of fusulinid taken after very diligent search is a Triticites dated as Virgilian by Mr. Garner Wilde, H u m b l e Oil a n d Refining Company (letter to Cooper, 20 March 1962) (Plate 16: figure 1).
Wolfcamp Series
T h e rocks overlying the Gaptank Formation in the Glass Mountains were named the Wolfcamp Formation by Udden (1917:41). Since the forma- tion was named, it has suffered from disagreement among workers as to its age a n d its boundaries.
Wolfcampian rocks have been called the Wolfcamp Series, a n d they have been placed as the earliest major division of the Permian System in the United States. Rocks deposited in Wolfcampian time, thus, have a great interest, and the Wolf C a m p Hills are the most significant reference section for these rocks and their contained fossils (Plate 1: figure 3; Plate 2: figure 2).
T h e Wolf Camp Hills were not a happy choice from which to select a name with such wide rami- fications. T h e Wolf C a m p Hills contain only a small part of the rocks laid down in the complete series called Wolfcampian, a n d the faunas of the type Wolfcampian rocks hithertQ have been poorly known. T h e present work is the first extensive paleontological study of the type Wolfcampian fauna.
In the Glass Mountains, Wolfcampian rocks oc- cur across the entire mountain front, usually in low foothills except for an interval between the east end of the Wolf Camp Hills and the Fort Stockton-Marathon road (U. S. Highway 385). T h e sequence in the Wolf Camp Hills now has become famous in spite of o u r ignorance of details of its faunal succession.
Udden used the name "Wolfcamp Formation"
for the generally shaly sequence exposed in the western part of the Wolf Camp Hills. U d d e n (1917:
29) applied the name to his beds 10—26 of section 7 and gave die thickness as 448 feet. T h e section rested on his bed 7 (= bed 2 or the Gray Lime- stone of P. B. King) and was capped by a thick bed of conglomerate ( = Hess conglomerate = Lenox Hills conglomerate of Ross). T h e Uddenites- bearing shale and the Gray Limestone of King were part of the Gaptank Formation. Bose (1917:
17 and Tables 1 and 2) placed the Uddenites-bear- ing shale in the Permian, thus including the Gray Limestone with it. King (P. B., 1931:54) recognized Udden's and Bose's interpretation of the forma- tion, b u t in the western part of the Glass Moun- tains he assigned to it rocks of different character, mostly conglomerates. King also discovered a con- glomeratic sequence in the Hess Ranch Horst that he correlated with the Wolfcamp Formation. Later the Uddenites-bearing shale was excluded from the formation by P. B. King (1938:79) when Plummer and Scott (in P. B. King, 1938:79) demonstrated that its ammonites are exactly like those of the Cisco Series in north-central Texas.
T h e first revision of the Wolfcamp Formation was made when J o h n E. Adams and collaborators
(1939) raised the formation name to that of a series. Jarvis (1957:4) studied the Wolfcamp For- mation along the Glass Mountains front and recog- nized that the Wolfcamp Formation of the type region was unlike that in the western part of the mountains. H e likened the latter western part to the Hess Formation of Udden. Ross (1959) re- studied the Wolfcamp Formation as defined by P. B. King and made a drastic revision of it. T h e sequence in the Wolf Camp Hills, the type Wolf- camp Formation, was renamed by Ross the "Neal- ranch Formation" 3 with boundaries from the top of the Gray Limestone of P. B. King ( = bed 2 of King's section, 1931) to the Hess conglomerate.
Rejection of the Gray Limestone (= bed 2 of P. B. King) from the Wolfcamp Formation was based on work of Sellards (1932:148) and evidence resulting from his own work on fusulinids. T h e conglomeratic sequences in the western part of the Glass Mountains, in accordance with Jarvis' views, were discovered to be faunally, as well as lithically, distinct from the Neal Ranch Formation. Accord-
ingly, these conglomeratic beds were named the
"Lenoxhills Formation" 4 and were stated to over- lie the Neal Ranch Formation.
Overlying the Lenox Hills Formation, rocks hitherto regarded as early Leonardian in age are grouped into a formation now placed in the Wolf- camp Series. T h i s formation, the Skinner Ranch
(Cooper and Grant, 1964), contains many fossils related to the Wolfcamp below and some that link it to the upper part of the Pennsylvanian Gaptank Formation as well.
N E A L R A N C H FORMATION
T h e Neal R a n c h Formation has its type section on the Bill Neal Ranch, at the Wolf Camp Hills 13 to 14 miles northeast of Marathon. Ross's type section was made not far east of King's section, near that of Udden, b u t he does not include the Gray Limestone as King (1938) did in his later definition of the formation. W e do not agree with this action of Ross and hereby restore the Gray Limestone (bed 2 of P. B. King) to its position at the base of the Neal Ranch Formation. O u r reasons for restoration of this member to its old position are explained below in a discussion of the Wolfcampian faunas.
Considerable difficulty is experienced, in the Wolf Camp Hills, in making a continuous section of the Neal Ranch Formation that conforms to prior published sections. King's (P. B., 1931:54) section made in the western part of the hills does not conform with those prepared by Jarvis, Cooper, or Ross. T h e place selected by King for his section does not give as complete a sequence as can be obtained along the south-flowing branch of Geolo- gists Canyon, where Ross (1963a:21) measured his section. None of the geologists subsequent to King has been able to confirm his system of numbers.
Although we measured sections in the same places as King, Jarvis, and Ross, our sequence is not precisely like theirs. Localities cited by Batten, Finks, and Yochelson in their works on the gastro- pods and sponges frequently refer to bed 9 or beds 9-12 of Cooper. These are not the same as the numbers in King's section; bed 9 of Cooper is bed 12 of King.
s Originally written in this form by Ross but later revised by him (Ross, 1960) to "Neal Ranch."
1 As with the lower formation, Ross originally combined the two elements of the name.
KING
JARVIS
COOPER
BEDS 9 - 1 2
SHALE or COVERED
SANDSTONE LIMESTONE CONGLOMERATIC LIMESTONE
CONGLOMERATE
FIGURE 5.—Diagram comparing the section of the Neal Ranch Formation prepared by P. B. King with those prepared by Jarvis, Ross, and Cooper (ud=Uddenites zone; scale in feet).
Another difficulty arises from the fact that the Neal R a n c h Formation thins eastward. Conse- quently, the excellent section given by Jarvis (1957:
5) differs in thickness and sequence from that of Ross (1963a:21), which was measured east of Jarvis's locality, where the strata are thinner. W e offer our own section and a diagram comparing it with those of Jarvis, Ross, and King in an effort to make them all conform. I t is important that
the level of all Neal R a n c h fossils be located as accurately as possible.
T h e Neal Ranch Formation consists of 412-547 feet (composite section) of dark gray shale alter- nating with thin or massive beds of limestone, some of them swelling to interesting and important bioherms with unsuspectedly rich and varied faunas. A revised section of the Neal R a n c h For- mation is given below, and the important beds
are discussed in detail. T h e section is composite, because the sequence is not the same across the hills and a continuously exposed section of the beds cannot be found. T h e thickness of the basal limestone or Gray Limestone Member of P. B. King diminishes to the west of its thickest point, and the shale beds also thicken and thin. T h e sudden appearance of bioherms in the section also makes measurement difficult and uncertain. T h e section between beds 2 and 12 of P. B. King was measured in the west end of the hills, u p Geologists Canyon, and then at its first elbow, u p the hill to the north, ending with King's bed 12 ( = b e d 9 of Cooper).
T h e remainder of the section, which has no coun- terpart in King's measured section, was taken from bed 12 of King on the west side of the north branch of Geologists Canyon, from the second elbow to the base of the conglomerate on the hill slope 0.7 mile N 76° W of hill 5060.
T h e composite section of the Neal Ranch For- mation is as follows:
feet Hess Conglomerate
D. Predominantly shale with thin and thick layers of limestone ranging from a few inches to 6 feet (details given under the
units) 144 C. Biohermal limestone, shale, and cobbly lime-
stone conglomerate 40-75 B. Dark shale with occasional thin, scattered
limestone layers 178 A. Gray Limestone Member 50-100
412-547 Gaptank Formation (Uddenites-bearing Shale Member)
GRAY LIMESTONE MEMBER OF P. B. KING.—P. B.
King (1931:55) first used the name "Gray Lime- stone Member" for three beds that overlie the Uddenites-bearing Shale, his beds 2 to 4. In 1931 he regarded the Uddenites-bearing shale as the lowest part of the Wolfcamp Formation ( = h i s bed 1). In his section, bed 2 consists of 37 feet of gray limestone, which forms cliffs and is a con- spicuous physiographic feature in the Wolf Camp Hills, especially hill 5060, where it forms a high bluff that was thought by King to be limestone (but not exposed where the section was measured). Bed 4 also was assigned to the Gray Limestone, but this bed contains a distinctive fauna of marked Per-
mian affinities.5 Furthermore, on the n o r t h slope of hill 5060 a considerable thickness of shale in- tervenes between beds 2 and 4. Beds 3 and 4 are hereby removed from the Gray Limestone Mem- ber because of the distinctive character of the fauna of bed 4. Hereafter, in this discussion, only bed 2 of King will be called the Gray Limestone Member (Plate 12: figure 3).
Philip B. and R. E. King (in P. B. King, 1931) mapped the Gray Limestone across the Wolf Camp Hills and eastward to the Fort Stockton Road
(U. S. Highway 385). Later, P. B. King (1942:648) recognized that the Gray Limestone did not have this great lateral extent. Further studies of the fusulinids and detailed sections in the foothills northeast of the Wolf Camp Hills make it clear that the thick gray limestones so like the Gray Limestone Member at the base of the Neal Ranch Formation are really layers in the Gaptank For- mation. T h e Gray Limestone is thus confined to the Wolf Camp Hills.
T h r e e separate areas in the Wolf Camp Hills exhibit the Gray Limestone Member, the western- most area being the locality at which P. B. King measured his section and named the member. In the western end of the Wolf C a m p Hills several good exposures of this limestone occur. In the cen- tral part of the hills the limestone forms a promi- nent cliff capping hill 5060. A small butte in tne extreme eastern end of the hills is capped by a thick mass of dolomite identified by us as the Gray Limestone Member.
Westernmost Area: In the western part of the Wolf Camp Hills the Gray Limestone is exposed in Geologists Canyon, on an isolated butte on the west side of the canyon mouth, and in the hill slope west of the butte. T h e limestone can be fol- lowed u p the canyon for 0.4 mile to the first tribu- tary that comes into the main stream from the north (about where the 4650-foot contour crosses the canyon). T h e top of the Gray Limestone ap- pears in the canyon bed at this junction (USNM 701). T h e Gray Limestone, however, can be traced in the next gully from the south (the first indenta- tion of the 4700-foot contour upstream from the
5 King (1942:647) states that "The overlying gray limestone bed at the base of The Wolfcamp formation (beds 2 and 3) contains a few specimens of Schwagerina."