SCIENCE. V) 



A Set of Fifteen Specimens, to be used in connection with 

 Guide VII., will be furnished for $1.00. 



Orders for Specimens to accompany Guides ///., IV., V., VI , or 

 VII., should be addressed to Samuel Henshaw, Boston Society of 

 Natural History, Boston, Mass. 



Larger collections, and sets for students' use, containing ten, twenty, 

 forty, and sixty specimens of a single form, can be obtained by special 

 arrangement with Mr. Henshaw. 



Common Minerals and Rocks. {No. XII.) 



By W. O. Crosby, Assistant Professor of Mineralogy and Lithology in the 

 Massachusetts Institute of Technology. Illustrated. 4^ by 6 inches. 

 Paper. 200 pages. Introduction price, 40 cents. Cloth, 60 cents. 



This includes, first, a brief and simple account of the principal geo- 

 logical agencies ; second, descriptions of about twenty minerals of which 

 rocks are chiefly composed, and of all the more common and important 

 varieties of rocks ; and, third, an explanation of the leading kinds of 

 structure occurring in rocks, such as stratification, folds, faults, joints, 

 etc. This last section of the Guide is illustrated by forty figures, which 

 add very materially to the clearness and value of the text. 



Especial prominence is given to the easy identification of the com- 

 mon minerals and rocks, and to the constant association, in the mind, 

 of the rocks and rock-structures with the agencies by which they have 

 been formed. 



This little volume is not merely a guide to teachers, but it is also a 

 simple and logical presentation of the leading facts and principles of 

 structural geology, and is well adapted for class use. It is hoped, how- 

 ever, that teachers will base their instruction upon specimens of min- 

 erals and rocks, using this work more as a reference book than as a 

 text-book, in the hands of pupils. Natural science cannot be success- 

 fully taught with books alone ; and even the best books should sup- 

 plement, but not precede or take the place of, actual observation. 



Specimens to illustrate Guide No. XII, comprising the twenty 

 principal elements and minerals, are supplied in durable, covered boxes, 

 properly labelled, as follows : — 



I large specimen of each kind, 20 in all, labelled . . . $ .50 



5 smaller specimens of each kind, 100 " M ... 1.25 



10 " " " " 200 " " ... 225 



20 " " " " 400 " " ... 400 



