166 



THE BRISLINGTON CUTTING. 



% 





dull-red colour, though in the deeper frac- 

 ture the rock, especially where it is more 

 massive, is bluish grey. The dip is from 

 20° to 30° S. 10 E. It is much jointed and 

 troubled with little faults of small throw. 

 The main joints run N. 20° W. In the 

 Pennant were a number of large rounded or 

 oval shrinkage nodules similar to that which 

 stands on a pedestal at the Bath end of the 

 cutting. Similar shrinkage nodules were 

 found in the Millstone Grit of the Patch- 

 wa}' tunnel. 



The Triassic beds dip N. 70 W. at a 

 gentle angle of about 5°. The basement 

 beds immediately overlying the Pennant 

 are red and tolerably hard, and had to be 

 blasted in the engineering operations of the 

 cutting. From their hardness and the 

 similarity of colour, they were not readily 

 distinguishable at a little distance from the 

 Pennant itself. Examined with the lens, 

 the rock is seen to contain rounded or sub- 

 angular grains of sand cemented with cal- 

 careous matter containing a geod deal of red 

 oxide of iron. Treated with acid, the stone 

 effervesces freely. A hundred grains thus 

 treated yielded 57J grains of red sandy 

 residue. The material dissolved contained 

 no magnesium, and was" almost entirely 

 carbonate of calcium. There can be little 

 doubt that this carbonate of lime was 

 precipitated w^th the sand from the saline 

 waters of the Keuper Lake as they gradually 



