To these gentlemen, therefore, palaeontology is indebted for making it possible to describe one of the best collections of fossils made in arctic regions. On my way I observed a considerable quantity of the stone I had noticed at Iron Island, and I also saw many small pieces of limestone on the top of the summit about a thousand yards above the level of these."
The mountain forms a striking feature of the landscape, aud is composed of limestone dissolved to such an extent that the talus reaches almost to the top, which is very flat and consists of the ledge itself. 34;Through the occurrence of the Silurian rocks in Nettilling (Lake) (=Kennedy Lake), the discovery of the same formation at the upper end of FrobisherBay increases in value. The part of the island which has been seen [the north end to the middle of the east side] consists of renewed gray limestone in horizontal beds, and it represents a perpendicular wall 400 to 500 feet high throughout.
This sea wall is distinctly cut, and the beds appear thick and solid, but wherever their edges have been long exposed to the weather or in the hills and ravines of the interior, they divide into the inner strata. Here, therefore, there appears to be a complete break from the Laurentian to the Trenton, followed by another break paleontologically, iu the absence of the Cinciiinatian beds, and probably the lower horizons of the Upper. The species indicate the Trenton Limestone, and "are remarkably similar to the fossils of the Trenton Formation of the RedRiver Valley in Manitoba Eleven were previously found in the Manitoba Trenton, and nine are species common at East Selkirk and Lower Fort Garry ." This fauna also connects directly with that of Silliman's fossil mountain.
Mount Belongs in the Galena, and that the fauna is more closely related to that of the Minnesota region than to the Trenton or New.
CYSTOIDEA
BRYOZOA
In the American Museum of Natural History there are three specimens collected by E. Orthis {Hehertella?) hellarugosa Winchell and Schuchert, Geol. Common in the Galena or Trenton stage of Minnesota, this species is also abundant in the FrobisherBay area. Among the Arctic specimens, however, this variation tends towards the equalization and increase of the number of plications, while in Minnesota, bundling of the plications accompanied by the development of a conspicuous dorsal sinus, is the main tendency of variation.
In the same land, it is probably advisable to name the Arctic variation - those with. the more numerous and unequal, and the obsolete or nearly obsolete dorsal-sinus varieties. Occasional specimens occur with a few lamellae near the anterior margin, but generally they do not have these, their places being much occupied. Both are often tied in the same beds and then it is difficult to identify them.
Locality and Formation.-In the Lowville and especially in the Black Ever stages of Trenton in Minnesota and Wisconsin, Lexington, Kentucky, and in the Cincinnatian groupat Savannah, Illinois. Bhynchotrema ina'quiraJvis Wjnciiell and Schuchert (part), Geol.Minn.,Ill, Pt. This species was first described by Castelnau, who obtained his specimens from the "Niagnesian Limestone" of Drummonds Island. His figures show the characteristic concentric lamellae which are almost always present on these shells coming from Trenton, and this feature distinguishes them from those found in the Lowville and Black River stages.
The type is the characteristic Trenton form, while in the Cincinnatian groups its descendant R. ca/paxat is of large size, often large whorl, with pronounced concentric lamellae. incequivalvis is abundant. found. This shell is only an elongated variety of R. inmquivalvis, and appears to be a rare form in, Trentonof NewYork, but at Curdsville, Kentucky, it is abundant. inmquivalvis, the lamellae are well developed. However, it differs in various details, notably in the fact that it is always much larger. carpenteri also has the general aspect of small specimens of G.nasuta, but differs in the straight line, especially in the posterior one, which ends abruptly in the regular convexity of this part of the shell.
The outline of the valves varies further in the postventral region (wider) being more prominent and narrower here. Therefore, although he provisionally accepts that it is closely allied to Cyrtodontagibbera, Tamnot is satisfied that it will not turn out to be a Vanuxemianear V.abrupta.
164 PROCEEDINGS OF THE NATIONAL MUSEUM
This is one of the abundant species in the Silliman Fossil Mountain, and the United States extends from the Black Eiver group to the middle of the Cincinnatian group.
166 PROCEEDINGS OF THE NATIONAL MUSEUM
An example of this species measures nearly 3 inches in diameter, which is larger than the Minnesota specimens, but this is consistent with the larger size attained by Maclureas and Maclurina far north. Trochonema (Eunema) robbinsi Ulrich and Scofield, Geol.. Three examples of this species are present, of which only one is well preserved. The upper whorls of the best specimen correspond rather closely to the former, while the last whorl, with its relatively narrow peripheral band, is more in accordance with the latter species.
Note, however, that only the scaleless part of the specimen corresponds to T.(E,) similis, with the opposite side of the same whorls showing no trace of the ridge near the suture, which is highly developed and characteristic of T. similis.
168 PROCEEDINGS OF THE NATIONAL MUSEUM
However, it differs by its smaller growth, greater curvature and especially by the very rapid increase in cone. Billings gives the probable length of about 50 mm, which is very close to the protraction based on Arctic material. Clarke writes that the Minnesota specification. Man was probably no taller than 30 mm, but since his specimens are very small fragments, this estimate is probably shorter than the actual length. The depth of the sky. chambers decreases very little towards the top, the average being a. to where the shell has a diameter of 3.5 mm.
The clay specimens are usually compressed, and this is the condition of Arctic material, but the shell was circular in outline, with a very small central siphon. As shown by the figures, this species differs from other American onchocerazine in the large antero-j)osterior curvature of the ventral side of the shell. This is due to the rapid increase in air depth. chambers towards the ventral side, where they are about twice the depth of the back.
Cyrtoceras cornulum was initially thought to be a young stage of Oncocerasarcticum, but its section is more elongate-oval and the back is more rounded, the reverse being the case in the latter species. This species is much larger than any other in Trenton, United States, although it is much smaller than 0. magnum, a giant of the genus found in East Selkirk, Manitoba. The present form appears to be most closely related to 0. 0. whiteavesi Miller), but lacks the numuloid siphuncle of this species nor the sigmoid outline of the dorsal septa.
The head of this species resembles D.{P.)eboraceus Clarke. in the characters of the glabella and in the great bulging of the eyes. However, in J).{P.)goodridgii the eyes are still more elevated, the cephalon is smooth and devoid of all granulations, while the most marked difference is seen in the posterior outline of the head, which is . broadly rounded or subquadrate, with a short median projection. Named after Mr. To F. G. Goodridge of New York, one of the fossil collectors on Peary's 1897 expedition.
There are three examples of this type in the collection, none of which are complete, but all of which match well with the New York examples. So far, however, the distribution of the strata together with their fauna is well known only to the south and southeast of the Archean core, but to the west (Manitoba) and northeast (Baffin Country) they show direct communication. The Baffin Landfauna had an early introduction of Upper Silurian genera into the corals Halysites, LyeJlia, and Plasmo])ora. Fifty-seven percent of the Baffin Land species also occur in the galena of the regions just mentioned.
EXPLANATION OF PLATES
