42 NATURE STUDY REVIEW [9 : 2— Feb, 1913 



grained rock and is usually gray, black, green or red in color. 

 Slates are formed from fine-grained rocks, chiefly shales and 

 clays. They may be told from shales by their more perfect 

 cleavage, shiny surface on the cleavage face and their superior 

 hardness. Slate is used for roofing, for school slates, slate pen- 

 cils, blackboards, wash-tubs, for lining refrigerators, and has a 

 great many other uses. It is found especially in Pennsylvania, 

 Vermont, New York and Maine. 



The first thing to do on finding a rock is to decide into which 

 of the three groups it belongs. Not only should the texture and 

 the minerals of the rock be observed, but the structure of the rock 

 in the field should be observed, if possible, as it will be a great 

 aid in determining the rock. As soon as it is known into which 

 group the specimen belongs, the descriptions of the members of 

 the group should be applied to it. If it is an igneous rock it 

 will be found to fit intO' the table given above. If it is a sedi- 

 ment, there will be no difficulty in telling the conglomerates and 

 the sandstones, but it is harder to distinguish the limestones 

 and the shales, especially to tell them from one another. Since 

 the limestone is easily soluble in acids this test can be used to 

 distinguish them, if there is some acid at hand. A few cents' 

 worth of dilute hydrochloric acid purchased at a drug store will 

 be found to be a great aid in working with the sediments. But 

 sometimes shales are very calcareous and under such circum- 

 stances the ease with which they effervesce will aid in separating 

 them. There will also be considerable insoluble matter left if 

 it is a calcareous shale. Another feature of shales is their clayey 

 odor when moistened either by breathing upon them or by wet- 

 ting them. Shales are usually more finely laminated than lime- 

 stones. Only the more common kinds of the metamorphic rocks 

 have been mentioned because in a short time the list would have 

 become entirely too long for this short paper. 



The knowledge of a few of the common rocks is very useful 

 and important. Familiarity with a few will lead to the acquain- 

 tance with more and will give the student a better understand- 

 ing of the composition of the earth around him. The real student 

 does not stop with learning the few. They are merely the 

 stimulus to search for more information, for a wider working 

 acquaintance. It is sincerely hoped by the writer that all who 

 read this paper will be helped, and that all will unite in bringing 

 the children into a closer working relationship with the rocks 

 and minerals that are around them. 



