132 TOWN GEOLOGY. [TI. 



S.E. (Bangor) of the'Snowdon district of the Govern- 

 ment Geological Survey, which may be ordered at 

 any good stationer's, price 3s. ; and study it with me. 

 He will see down the right-hand margin interpretations 

 of the different colours which mark the different 

 beds, beginning with the youngest (alluvium) atop, 

 and going down through Carboniferous Limestone and 

 Sandstone, Upper Silurian, Lower Silurian, Cambrian, 

 and below them certain rocks marked of different 

 shades of red, which signify rocks either altered by 

 heat, or poured out of old volcanic vents. He will next 

 see that the map is covered with a labyrinth of red 

 patches and curved lines, signifying the outcrop or 

 appearance at the surface of these volcanic beds. 

 They lie at every conceivable slope ; and the hills and 

 valleys have been scooped out by rain and ice into 

 every conceivable slope likewise. Wherefore we see, 

 here a broad patch of red, where the back of a sheet of 

 Lava, Porphyry, Greenstone, or what not is exposed ; 

 there a narrow line curving often with the curve of the 

 hill-side, where only the edge of a similar sheet is 

 exposed; and every possible variety of shape and 

 attitude between these two. He will see also large 

 spaces covered with little coloured dots, which signify 

 (as he will find at the margin) beds of volcanic ash. If 

 he look below the little coloured squares on the margin, 

 he will see figures marking the strike, or direction 

 of the inclination of the beds inclined, vertical, hori- 

 zontal, contorted ; that the white lines in the map 

 signify faults, i.e. shifts in the strata ; the gold lines, 

 lodes of metal the latter of which I should advise 

 him strongly, in this district at least, not to meddle 

 with : but to button up his pockets, and to put into 



