194 NEW YORK STATE MUSEUM 



disrupting effects of changing temperatures are best seen where 

 several of them are associated." High altitude is also favorable 

 because in the dry, thin atmosphere the accumulated heat of the 

 day radiates rapidly at night. Of these features favorable to tem- 

 perature changes and exfoliation the ones notably deficient in War- 

 ren county are high altitude and aridity. 



Although Warren county is by no means in an arid climate, it is 

 nevertheless interesting to note that its location is in the dryest 

 part of New York State except the St Lawrence valley.^' The 

 average precipitation for the year is only 25 or 30 inches, and 

 hence the comparatively dry atmosphere of this region is important 

 so far as New York State is concerned, because under a dry 

 atmosphere a rock mass heats up more during the day and cools off 

 more during the night, thus favoring exfoliation. 



The isolation of the masses of igneous rocks should be mentioned 

 because their better exposure favors greater daily temperature 

 changes. 



It should also be stated that changes of 30 to 50 degrees between 

 day and night temperatures in this county are not at all uncommon. 



Finally what has been termed the " wedge-work of ice " should 

 be considered. So far as can be learned the greatest movement 

 of exfoliation slabs down the mountain sides is during the fall and 

 spring months and this is probably due to the fact that the cracks 

 in the rock are then pretty well filled with water which expands 

 on freezing and thus wedges off the already loosened slabs. 



5 Scanty soil and vegetation. As above stated, the passage of 

 the ice sheet across the region removed all soil, talus, and vegeta- 

 tion from the igneous rock elevations leaving the bare rock surfaces 

 favorable for exfoliation. Though none of the domes are at pres- 

 ent entirely free from vegetation there are, nevertheless, many large 

 barren surfaces, and what vegetation does occur is generally scant 

 like small scrub pine, growing out of the cracks in the rocks. The 

 surfaces of the domes are thus at present essentially barren and in 

 this regard favorable for exfoliation. 



^ Tarr's Physical Geography of New York State, p. 354. 



