60 NEW YORK STATE MUSEUM 



mountain district. Also it is well known that this great peneplain 

 was upraised from looo to 3000 feet about the close of the Mesozoic 

 or beginning of the Cenozoic era. 



As above stated (see page 46), there is good reason for believing 

 that much of the faulting, which has produced the larger existing 

 topographic features, took place subsequent to the development of 

 this Cretacic peneplain, and probably at the time of its uplift. 



Cenozoic history 



The existing surface configuration or relief of the region has 

 very largely been produced by the faulting and erosion of the up- 

 raised Cretacic peneplain. Most of the numerous tilted fault blocks 

 and ridges date from this time, and the streams, greatly revived 

 as erosive agents, have continued to the present time to carve out 

 the many channels, especially along fault lines. 



Late in the Cenozoic era came the Glacial epoch or Ice age when 

 all the quadrangle, as well as nearly all the State, was buried under 

 a great ice sheet. Many local details of the present topography are 

 due especially to morainic or glacial lake deposits in the valleys. 



Topographic influence of faults and rock character 



The profound influence of faulting upon the topography of the 

 region is very clearly brought out by an inspection of the accom- 

 panying geologic map and, after the descriptions of the faults in an 

 earlier chapter, no details will here be given. Suffice it to say that 

 nearly all the major relief features, such as the northwest-southeast 

 mountain ridges and many of the more prominent valleys, are due 

 to faulting. These ridges have been considerably modified by 

 weathering and erosion subsequent to the faulting. Aside from these 

 major features, many stream channels have been developed along 

 fault lines or zones of weakness. 



In contrast with the Adirondack region in general, and the North 

 Creek region recently described by the writer in particular,^ no 

 one of the Precambric rock formations may be said to stand out 

 prominently above the others against weathering and erosion. 

 Where the Grenville is notably developed in the Adirondacks, it 

 is the rule for its weaker members at least to occupy the valleys, 

 but within the Lake Pleasant cjuadrangle, the Grenville is neither 

 prominently developed nor does it contain much weak rock such as 

 limestone. Quartzites and hard gneisses make up the bulk of the 



1 N. Y. State Mus. Bui. 170. 



