ROCHESTER AND ONTARIO BEACH QUADRANGLES 9 



Toward the close of Lower Siluric time the land and seas were 

 becoming unstable. The culmination was finally reached with the 

 Taconic revolution 1 which began near the close of the Lorraine and 

 the great disturbance which followed resulted in the Green mountain 

 uplift. The results of this mountain building were of great import- 

 ance and affected the region from the St Lawrence to Alabama. 



In New York the whole eastern portion of the State became land. 

 With the elevation of the land, folding and a planing down of the 

 surface began. Thus in the sections where folding and erosion were 

 the most extensive, this planing down had the effect of bringing the 

 older formations to view. Much of these folded and eroded rocks 

 were included in the old term " Hudson River group," formerly- 

 supposed to be entirely above the Trenton, but which Dr Ruede- 

 mann 2 has shown includes beds which range in age from middle 

 Trenton to the close of the Lorraine. 



The western effect of this uplift in New York seems not to have 

 extended farther than the east end of Lake Ontario, since in 

 this vicinity we have the Oswego sandstone which is the lowest 

 member of the Upper Siluric, following directly and in perfect 

 conformity to the Lorraine shales. 3 The transition from the Lor- 

 raine beds to the Oswego sandstone is one of importance, for it 

 involves the question of a possible equivalency herein to the Rich- 

 mond beds of Ohio and Indiana. These latter beds which are above 

 the Lorraine contain recurring Trenton fossils. The Oswego sand- 

 stone is almost nonfossiliferous and thus paleontological evidence 

 for correlation is wanting. In the light of our present knowledge it 

 seems best to regard the Richmond beds as deposited just as the 

 Taconic revolution was in progress and just after the Lorraine 

 deposits were brought to a close in eastern New York. These 

 changes of conditions were most marked in New York and under 

 their influence the Lorraine fauna disappears ; but farther west the 

 conditions appear to have been favorable for the development of the 

 Richmond fauna.* 



i See Ulrich & Schuchert. N. Y. State Paleontol. An. Rep't. 1901. p. 646. 



2 N. Y. State Mus. Bui. 42. 1901. p. 567. 



3 Geol. N. Y. 3d Dist. 1842. p. 61. 



4 The question involving the equivalency of the Oswego sandstone and the Richmond beds, 

 as well as the system in which they belong, is one which requires considerations of such detail 

 that it can not be discussed within the scope of this paper. The Oswego sandstone is therefore 

 retained as a member of the Upper Siluric, although there is evidence which may show that all 

 of the Oswego and probably part of the Medina could with propriety be included with the Lower 

 Siluric. 



