440 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This stage embraces the two groups III. and IV. Both of them 

 are mainly alternating depositions from quiet waters of argillaceous 

 and arenaceous mud ; group No. III. occasionally possessing more 

 or less of limestone, either minutely disseminated or in seams. It 

 has been shown elsewhere that the fossil-relations of the different 

 parts of this stage are nowhere unfrequent, but are remarkably close 

 between the Hamilton and Chemung Rocks. This is, therefore, a 

 natural stage. 



Upper Stage. — This stage includes the numerous and varied strata, 

 of great thickness, in the southern districts of New York, which have 

 been associated together under the name of the Catskill Sandstones. 



This is a safely-designated horizon. With perfect conformable- 

 ness, there is here a sudden change of lithological constitution. In- 

 stead of an impalpable mud, we find boulders, pebbles, grit, and red 

 sandstone, with occasional shales. The fossils of the middle stage 

 have all disappeared, and two new Dimyaria (Cypricardites angus- 

 tata and C. Catskillensis, Vanuxem) are the only representatives of 

 the molluscan type remaining ; while some of the fish and plants be- 

 longing to the Old Red Sandstone of Europe are present in moderate 

 numbers. 



Inferential Propositions. 



In possession of the stratigraphical details contained in the c Synop- 

 tical View ' and in the preceding pages, it seems desirable to bestow 

 some attention on historical geology, and to pronounce, if possible, 

 on some of the influences which have resulted in the present aspect and 

 condition of the palaeozoic sedimentary beds of the State of New York. 



Of these influences or conditions, two, which are not the least 

 important, according to the views of many geologists, may be summed 

 up in the following short propositions : — 



1. That from the Potsdam Sandstone to the summit of the Car- 

 boniferous rocks, these strata were laid down in comparative quiet ; 

 subject to secular oscillations — vertical, variable, perhaps constant, 

 and which led to considerable superficial changes. 



2. That their elevation, foldings, fracture, and metamorphism were 

 effected after the deposition of the whole, in a single prolonged 

 transaction, and principally in a N.E. and S.W. direction along the 

 present Appalachian ridges and their continuation from Labrador to 

 the Gulf of Mexico. 



From these statements the Professors Rogers dissent ; but prin- 

 cipally as regards the period at which the great crust-movement 

 spoken of in the second proposition took place. 



I shall first endeavour to support the propositions just laid down, 

 and shall afterwards address myself to the views of our able Ame- 

 rican brethren. 



I. With regard to the first proposition — 



1 . This is made very probable, if not proved, by an examination of 

 the uniting planes of coterminous sections or sets of beds. With 

 rare exceptions, they are all undisturbed and conformable in New 

 York, as may be seen through the whole ample series of palaeozoic 



