64 OUTLINES OF FIELD-GEOLOGY PART i 



(3d) Fine-grainedhaving a dull, exceedingly close 

 granular texture, which may pass into the fine v 

 the crystalline amorphous rocks on the one hand, and of 

 the fragmcntal rocks on the other. Many limestones 

 and felsites show this texture. 



As some of these textures characterise rocks of very 

 different geological structure and origin, they evidently 

 must be used with caution as a means of identification. 

 When there is room for doubt, other characters should 

 be looked for, and final appeal may have to be made to 

 the microscope. But cases will from time to time arise 

 when even with the help of that instrument no satis- 

 factory opinion can be formed as to the nature of a rock. 

 Especially is this true where the stone has undergone 

 some degree of decomposition. 



iii. FRAGMENTAL (C/as/if) composed of fragments of 



Fie. 9. Piece of conglomerate, showing the characteristic rounded 

 aspect of the component parts of many fragmental rocks. 



pre-existing rocks or minerals. As rocks of this type 

 are mere mechanical mixtures, they present an endless 

 variety, both in composition and texture. In the vast 



