LI BRAKY 



UNIVERSITY OF 



CALIFORNIA. 

 V= 



PART III. 



LITHOLOGT. 



CHAPTER I 



DETERMINATION OF ROCKS. 



Texture Structure Fracture Lustre Hardness and Efferves- 

 cence Specific Gravity Eeactions in the Wet Way Blow- 

 pipe. 



General Remarks. The kinds of rock of which the crust 

 of the earth is composed are as various almost as the 

 rocks themselves. Eocks coming under the same de- 

 nomination, such as clay, sand, and so on, have been 

 formed during all geological periods, but vary more or 

 less in their minor characteristics. This is owing mainly, 

 .as regards sedimentary deposits, to differences in the 

 kind of the rocks (and the relative quantities of each 

 kind) from which they have been derived that is, in 

 any area, and at any time subject to denudation. The 

 resulting deposits differ accordingly, perhaps not so much 

 .that it shall always be possible to -examine a specimen 

 and say at once, " This belongs to such and such a for- 

 mation," but it can be done in very many instances; and 

 when it cannot, Palaeontology must furnish the additional 

 .evidence. The eruptive and intrusive rocks vary also 



