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NEW YORK STATE MUSEUM 



Let us iioav inquire into the condition of the early surface of 

 the region and the method of erosion which has produced the 

 peneplain surface, after which we may discuss more in detail the 

 erosion accomplished during the present cycle. 



The Paleozoic coastal plain. In discussing the origin of the vari- 

 ous geologic formations of this region it has already been pointed 

 out that each of the more extensive ones at any rate must have 

 been deposited over the entire region, overlapping the earlier ones, 

 and extending up on the old shore which was then formed by the 

 Precambric and early Paleozoic rocks. The later formations spe- 

 cially, such as the Hamilton, Sherburne, Oneonta and Catskill 

 sandstones were made of material directly derived from the crys- 

 talline rocks of the Adirondacks and Laurentides, and the meta- 

 morphic sediments of the Appalachian old land. It is easily seen 

 that there is no other likely source of these sediments and that 

 hence each one must in turn have overlapped the preceding ones 

 and come to rest directly on the shelving surface of the old land. 

 With their present dip of 135 feet to the mile the base of the 

 first red sandstones of this region ( the Oneonta ) would be car- 

 ried 5000 feet above the sea in the region of the Mohawk and more 

 than 15,000 feet in the central Adirondack region. As the present 

 dip of the strata is probably much greater than the original dip 

 of deposition and as the Adirondack region has suffered much 

 erosion in Postpaleozoic time, there is no reason to believe that 

 the Adirondacks were wholly covered by the Oneonta and Catskill 

 strata, though they probably reached far up on them. A clear 

 comprehension of the former extent of the strata of this region 

 helps one to realize the enormous amount of erosion which the 

 region has suffered since Paleozoic time, as well as the length of 

 the lime consumed in the process. Compared with this tremen- 

 dous erosion the formation of the Schoharie valley during the 

 present cycle of erosion is a very insignificant result, scarcely more 

 than a scratch on the surface of the ancient peneplain. 



Development of drainage lines. After the coastal plain of Paleo- 

 zoic strata emerged, by the southward and westward retreat of 



