
254 STRUCTURAL AND FIELD GEOLOGY 
| definite walls, showing much the same structure through- 
| out, and varying but little in width or in the nature of their 
. contents. Lastly, fissure-veins, instead of occurring as more 
or less well-defined lodes following some determinate direction, 
may form a close network of reticulating and intercrossing 
veinlets and threads, occupying all the cracks and crannies 
of a much divided and shattered rock-mass, 

