238 NEW YOEK STATE MUSEUM 



In addition to the more technical books described above, there 

 are many accurate and important works written for popular read- 

 iDg both at home and abroad. The number of these is constantly 

 increasing and they can be found in the large libraries or obtained 

 through the book sellers. 



Field Work 

 outcrops 



There are in general two classes of geologic strata, the hard 

 and the soft. In New York the hard strata include all rocks 

 older than the Cretaceous. The soft include the formations of 

 the Cretaceous, Tertiary and Quaternary. Almost everywhere 

 the hard rocks are overlaid by soft deposits, usually of Quarter- 

 nary age, so that in any locality there is generally both hard and 

 soft geology. 



The hard geology is probably best for the beginner to take up 

 first, where he has a choice between the two. In Dana's Manual 

 of Geology and Sir Archibald Geikie's Outlines of Field Geology, 

 detailed directions are given for methods of study among the hard 

 rocks. 



The most important habit to be cultivated by the beginner in 

 geology, is that of recognizing outcrops when they occur, or in 

 their absence, of determining by surface indications the character 

 of the rock which underlies the soil. 



The beginner must form early, the habit of distinguishing loose 

 fragments or boulders from ledges or outcrops, and in regions 

 devoid of outcrops must study carefully the stone fences for frag- 

 ments of the local rock. The fences as a rule represent the aggre- 

 gate of loose rock fragments gathered from the surface of the 

 agricultural lands and these fragments have usually come from 

 the underlying rock. In parts of western New York, over the 

 soft Salina shales no fragments of local rock are found because 

 it decomposes into clay. There the fences are formed of small, 

 hard cobblestones chiefly derived from the granite and gneiss 

 rocks of Canada and brought to their present resting place by the 

 great ice sheet, i 



