GENERAL DISCUSSION. 6 
limestone bands, especially toward the top, which is formed by a bed about 4 feet thick 
that is extremely rich in bryozoa. This bed has afforded most of the bryozoa described in 
this paper. The limestone layers are often composed almost entirely of fragmentary bryozoa 
cemented together. The upper division of the shales is less calcareous and much less fos- 
siliferous than the lower. It also contains a very different fauna, the prevailing species 
being peleeypods, ostracods, and trilobites. Toward the top of this division fossils become 
still rarer and seem to disappear altogether as the basal layers of the overlying Lockport 
dolomite are reached. 
Since the publication in 1852 of Volume II of the Paleontology of New York, the bryozoa 
of the Rochester shale have received little attention. At that time Professor Hall described 
a large number of species from the classic locality, Lockport, N. Y. This work was remark- 
ably well done for that date and the methods of study then followed. In the majority of 
instances the student has little difficulty in identifying the various species. About a third 
of a century later Mr. E. N. S. Ringueberg added a few new species to the described fauna. 
These two men are the authors of practically all the forms so far described as originally 
from this shale. However, neither of them studied the internal characters of their species 
nor gave definite measurements to any extent, and since the correct generic identification 
depends on internal rather than external features further work on the fauna is desirable. 
It is, therefore, the object of this paper to figure and describe the known species, as well as 
new forms, using modern methods of description. 
The Niagara escarpment of western New York and Ontario furnishes numerous localities 
where natural exposures show the f ossiferous shale. In the vicinity of Lockport, N. Y., 
the two "gulfs," which indent the escarpment, afford excellent collecting ground, and here, 
especially in the vicinity of the Erie Canal, much of the material on which this paper is based 
was procured. Especially fine slabs and washings were obtained in the vicinity of the pulp 
mills along the Erie Canal. The beautiful preservation and the variety of specimens upon 
these slabs are brought out in Pis. XXVIII to XXX. At Lockport and localities in west- 
ern New York in general, the specimens weather out in an excellent state of preservation, so 
far as external characters are concerned, but on account of the presence of iron pyrites in 
the shales the internal features are sometimes destroyed. 
At Rochester, N. Y., the type locality of the shale, a different style of preservation 
obtains. In the examples found here the internal features are sometimes obscured by a 
slight silicification, and caustic potash must be used freely on the specimens to remove the 
clay, which often obscures the exterior features. Washings containing many or good free 
specimens are seldom to be found at Rochester, and the thin limestone layers, although 
containing numerous fossils, are generally so covered with a hard clay that caustic potash is 
necessary to expose them. At Middleport, N. Y., the limestone layers are sometimes made 
up almost exclusively of fragmentary bryozoa in an excellent state of preservation, as is 
shown by the small slab figured in PI. III. 
In the Niagara Gorge « the banks and railroad cuts afford a few good exposures, where 
the bryozoa-bearing shale is well exposed, and as a result a considerable number of species 
may be found. Here the preservation is essentially the same as at Lockport. The Silu- 
rian section is best seen on the American side along the cuts of the New York Central and 
Hudson River Railroad. The strata dip southward, while the railroad rises in the same 
direction, with the result that the various formations are crossed in ascending order going 
toward the Falls. In making the railroad cut, several mounds were left which now form 
good collecting ground. One of these mounds is on a level with the bryozoan bed, and here 
numerous specimens may be had. At most places along the gorge, however, the Rochester 
shale, although well exposed, is inaccessible, as is shown in Pi. II, facing page 4. 
In Ontario the principal localities from which bryozoa were obtained for study are 
Grimsby, Hamilton, and Thorold. Here the Rochester shales become somewhat sandy 
a The geology of this vicinity has been well described and illustrated by Doctor Grabau in his " Guide 
to the Geology and Paleontology of Niagara Falls and Vicinity " (Bull. New Yoik State Museum, No. 
45, 1901), to which the teader is relerred for a mere complete discussion. 
