l8g3.J FAIRCHILD — GEOLOGICAL HISTORY OF ROCHESTER, N. Y. 221 



Devonian ages, when by the slow uplift of the land northward this 

 Silurian sea-border region was permanently elevated above the 

 Devonian sea. Immediately rock formation ceased and rock destruc- 

 tion began. Since that day, and for an immense duration of time, 

 the history of our re-jion has been wholly one of degradation. This 

 was by chemical decay and disintegration under atmospheric agencies, 

 erosion by rain and streams, the loosened material bemg borne off to 

 the sea to form the marine sediments, now uplifted as rocks of later 

 ages, or still forming in the oceanic waters. How long could this have 

 lasted ? We can gain a faint idea of the immensity of the time by 

 enumerating the formations which have accumulated since the Niagara 

 period : the remainder of the Upper Silurian formation with about 

 3,000 feet of shale and limestone ; the Devonian with 20,000 feet of 

 shale and .sandstone and limestone, and four well marked periods ; 

 the Carboniferous with its three periods and 20,000 feet of sediments ; 

 the Triassic with 15,000 feet of sediments; the Jurassic with 5,000 

 feet ; the Cretaceous with 30,000 feet ; the Tertiary with three 

 periods and 20,000 feet; a total of over 100,000 feet of slowly 

 forming marine sediments. Geologic time, that is, since the ocean 

 existed, has been estimated by geologists from 20,000,000 to 

 200,000,000 years. Probably the time since the Niagara is about 

 one-half of the whole. During all these ages the work of destruction 

 was carried on over this region, and a great depth of rock was doubt- 

 less removed. The topography or surface configuration was unlike 

 that of the present, and this northern part of the continent stood in 

 the Tertiary at a higher altitude. The drainage must have been 

 very different and much more vigorous. There may have been in 

 later time a streain having partly the same hydrographic basin as the 

 Genesee, but of its course and features nothing is definitely known. 

 Lake Ontario was not then in existence. There were no lakes and 

 no cataracts in all this region, as they belong to the adolescent phase 

 of streams. The character of the surface material was unlike that of 

 to-day, being a true soil of decomposition, not a sheet of transported 

 matter or drift. 



The characteristic land life of the several ages came into being, 

 flourished, culminated and disappeared : Amphibians in the Devonian 

 and Carboniferous ; true reptiles in the Carboniferous and Reptilian ; 

 Mammals and Birds in the Reptilian and Tertiary. During the 

 Tertiary the Mastodon and Mammoth roamed over this region, with 

 other strange creatures. No good evidences of man are found. 



