xiv SURFACE GEOLOGY 19$ 



ravine, has had many a joint under hit eyes. They 

 are fa the quarryman and miner, by whom their 



:ions are always well known, seeing that they 

 determine the course along which quarrying and many 

 mining operations proceed When the geologist it 

 engagr<i in hilly or mountainous ground, among crags 

 ami ruck pinnacles, or on exposed coast -cliffs, he should 



not fail to note with some care the trend of the different 

 joints. He will soon find that they are apt to run in 

 two main directions. And a little further examination 

 will usually enable him to connect the forms of the cliffs 

 with the lines of joint He will observe how one set of 



runs parallel with the face of a cliff, and i 

 across by another series, and how the quadrangular 

 buttresses of rock, which may shoot up perhaps into spiry 

 pinnacles at the top, have their shape first given to them 

 1>\ the intersecting lines of joint (Fig. 78, and also Figs. 

 12 and 13). 



