394 
[Assembly 
bristles grew on it. The fin is about ten inches long and imperfect. 
It probably belongs to an undescribed genus of sauroid fishes. 
The thickness of this rock on the Tioga exceeds 400 feet. Owing 
to an uplift producing an anticlinal axis near Covington, the thickness 
of the rocks between the coal measures of Blossburgh and the INew- 
York fine, has been over rated. 
Passing westward the redsandstone is not equally a guide to the proxi- 
mity of the carboniferous strata, as just noticed, it thins out rapidly in 
this direction, and I have not yet identified it beyond the Genesee. At 
this place, near the mouth of Dyke creek, at Wellsville, it contains 
fragments of bones resembling those at Tioga. They appear as if 
transported with the materials of the rock, which consists of sand or 
fine pebbles, bearing evident marks of the wearing action of water. 
This rock forms the limit between the Silurean and Carboniferous 
systems and may be regarded as one of the most important of the 
whole series. All the coal deposits of any importance will be found 
above this rock, and from what we now know, none of them extend 
within the limits of our State in the Fourth District. When this rock 
shall have been farther examined, and its characters and associations 
better defined, it will doubtless prove to hold the same relations to all 
our coal fields, as its equivalent does to the same rocks in England. 
Since the publication of Mr. Murchison's work, we have been ena- 
bled to establish with great certainty, the analogy of our rocks with 
those of the Silurean system, as developed in England and Wales. 
In this country, however, the greater undisturbed range, and appa- 
rently better developement of particular members, with more numerous 
species of organic remains, enables us to limit our subdivisions within 
narrower bounds, and thus offer greater facility for the study of parti- 
cular groups. Since, then, all obscurity in this system of rocks is re- 
moved, we may go on with more confidence and satisfaction in our ex- 
aminations, every observation adding to our convictions of the perfec- 
tion of order of arrangement, and to our admiration of the grandeur 
and beauty of the whole. The publication of Mr. Lyell's Principles 
of Geology was termed an era in the science, and the same may be 
said of Mr. Murchison's work ; it forms an era and an important one 
in the development of the older fossiliferous rocks which have been 
so long enveloped in obscurity. It offers inducements to the study 
