120 



LITHOLOGICAL GEOLOGY. 



(3.) Forms and faults of veins and dikes. — Fig. 116 represents 

 two simple veins or dikes (a a and b b) intersecting stratified rocks. 

 Fig. 117, a net-work of small veins. 



Fig. 119. 



Fig. 118. 



Fig. 118, small veins of quartz intersecting gneiss, — the mass five feet square. 

 The veins do not all cross one another, and correspond to the cracks which 

 result from contraction, as by sun-drying or cooling, rather than to those of 

 any other mode of Assuring. 



Fig. 119. Two veins a a', presenting some of the common irregularities of 

 mineral veins in size, the enlarged parts containing mostly the ore : a is faulted 

 "by another vein b, which is of subsequent formation. 



Fig. 120. 



Figs. 120, 121, 122. Examples of granitic veins of very large size in a 

 gneissoid granite, showing their subdivisions and various irregularities (taken 



