XII! SCl 177 



const: are usually very inconstant, that 



they arc a ken out capriciously into concretions 



ami thin away rapidly, and that they often possess a 

 red or crumpled character, which can be 

 seen in large contortions on the face of a mountain, and 

 descends even into such minute forms as can only be 

 observed with a microscope. It is evident that rocks 

 presenting such remarkable characters must offer many 

 ti of difficulty as well as of interest to the field- 

 geologist 



I M beginning the examination of a region of foliated 

 rocks, the observer may of course dismiss from his mind 

 the idea of receiving help from organic remains. In rare 

 instances, indeed, traces of fossils have been obtained from 

 ose rocks, or from altered limestones associated 

 with these rocks. But this is an accident not to be 

 counted upon. With the absence of pabeontological 

 assistance, there is also a great lack of stratigraphical 

 aids, so that the learner may be led, after a few efforts, 

 to give up as hopelessly impracticable the task of making 

 out any structure of the ground Yet he will be surprised 

 in the end at what can be done by patient observation of 

 the puzzling masses. He may be led to collect their 

 minerals, and if so, will find them in many places, 

 particularly among the limestones, to be a rich store- 

 house of beautiful and interesting varieties. By degrees 

 he will discover that particular rocks are distinguishable 

 by special minerals, and he may even be able to trace 

 such rocks or bands of rock across the mountains by 

 means of these peculiar minerals, which will thus be put 

 to the same kind of use as fossils are by the stratigrapher. 

 N 



