92 FIELD GEOLOGY. 



abouts. The best observable edge is thus obtained ; 

 and if the specimen is to be preserved, it may with ad- 

 vantage shew one weathered side, and should not be too 

 large for portability. 



Texture. The rock or mineral is first examined for 

 " texture ;" this may be very apparent, but if not readily 

 decided, it must be observed with a pocket lens of one, 

 two, or three powers as may be found requisite. This 

 point should if possible be settled ; but when doubtful 

 under the lens, look for lines of varying colour as signs 

 of stratification. The texture may be either 



CRYSTALLINE in which the crystals are uniform 



and apparent, as in Quartz 

 Confusedly-crystalline as in Granite 

 Sub-crystalline as in some Limestones 

 GLASSY resembling Glass as in Obsidian. 

 COMPACT or homogeneous as in Flint 

 GRANULAR made up of distinct and somewhat 



rounded grains as in Sandstone 

 LAMELLAR \ consisting of thin plates or layers, the 

 LAMINATED > laminae being in the lines of bedding 

 FOLIATED ) as in Mica, Schist, &c. 

 CLEAVED consisting of thin plates or layers, the 

 laminae being transverse to the lines of bedding 

 as in Clay-slate 



FIBROUS resembling fibres as in Fibrous Gypsum 

 EARTHY soft and friable as in Shale 

 PORPHYRITIC enclosing larger embedded crystals. 



as in some of the Cornish Granites. 

 VESICULAR full of little cells or versicles as 



in Pumice. 

 Structure. The " structure " also of rocks must be 



