and even generally unsuspected. That they do underlie the 

 whole region can easily be proven by digging wells or sinking 

 shafts anywhere to a moderate depth through the soil and loose 

 material, when solid rocks are sure to be encountered. Plate III 

 shows one of a vast number of instances where this universal 

 state of affairs can be seen, viz., soft, loose earth or soil above, in 

 which trees and vegetation in general thrive; firm rocks ar- 

 ranged in layers below. 



Kinds of Devonian Rocks in Southern New York. 



Shale. — While examining the rocks in any quarry or natural 

 exposure in southern New York the student will observe that 

 certain layers are quite thin, soft, and contain but little grit and 

 are so fine in texture that the ordinary hand glass fails to reveal 

 their component particles, save perhaps a bit of mica here and 

 there. They can often be whittled with a knife and used as slate 

 pencils without scratching the slate. These are termed shaly 

 layers, or shale. 



Sandstone. — Thicker, harder layers, usually very "gritty" 

 and polishing or scratching a knife- blade when rubbed upon it, 

 and containing grains of sand often large enough to be seen with 

 a hand glass, or even the naked eye, are called sandstone layers 

 or sandstone. 



Calcareous layers, or limestone. — Hard layers, often thick and 

 containing fragments of shell-fish and effervescing or bubbling 

 when touched by a drop of strong acid are termed calcareous 

 layers. In southern New York they are generally too impure to 

 be properly termed limestone. They are sometimes called "fire 

 stone." By long exposure to the atmosphere the lime (calcium 

 carbonate) leaches out and the rock is left a soft dark brown or 

 black crumbling mass, often retaining the casts or impressions of 

 fossil shells. 



Conglomerate. — A layer or bed composed of large pebbles 

 (generally large white quartz pebbles) cemented together by 

 other material is called a pudding stone or conglomerate. 



