73 



DEPARTMENT OF MINERALOGY. 



INTRODUCTION. 



While the Biological Sciences deal with the forms of life that Introduc 

 have existed or still exist on the globe, it is the province of tlon * 

 Geology to trace and correlate in historical sequence the physical 

 changes that the earth's crust has undergone under the influence 

 of volcanic forces and the strains resulting from the contraction 

 of the globe, as well as of the not less potent agency of water in 

 its various phases of rain and river, sea and ice. The mineralo- 

 gist, on the other hand, deals with the nature and characteristics 

 of the materials that undergo these changes. It is for him to 

 investigate, to discriminate, and to classify the separate sub- 

 stances that are mingled and massed together to form a rock, 

 or that in an isolated condition may be met with in cavities 

 or veins, or as transported bodies. Substances of this kind, 

 which, when isolated, are homogeneous and definite in their com- 

 position and character, are minerals. In a block of granite the 

 separate minerals that are mingled to form its mass are quartz, 

 felspar, and mica, and they are usually distinctly visible and 

 recognisable side by side : in rocks of finer grain, however, the 

 discrimination is not so simple, and requires the aid of a lens 

 or microscope. The result of the study of rocks, and of their 

 component minerals, has been to show that the great mass of 

 the earth's crust is formed of aggregations of minerals belonging 

 to a very small number of the types that have been deter- 

 mined by the mineralogist. 



The minerals, on the other hand, that occur either as oc- 

 casional or as habitual rock constituents, present the great 

 variety, and, when arranged, the logical sequence which 

 give to a mineralogical collection its many-sided interest. 

 For the complete study of a mineral the mineralogist has 

 to look beyond its merely physical aspect and character ; 



