ifOTES ON TRIAS DYKES. 163 



parallel sides of the Dyke are due to the fact, that it was 

 originally matter filling-in a fissure or crack. At the time the 

 ■ conglomerate was being deposited, the Carboniferous Limestone 

 gaped slightly, in certain definite directions, and the fissures were 

 filled in with the materials of the conglomerate, which have set 

 into a hard compact mass. The Limestone is cut ap by joints 

 which have made it a comparatively easy prey to denuding 

 agencies, and hence it comes that the Dyke stands out prominently, 

 while the Limestone has been removed from around it. The 

 direction of this Dyke is N. and S. (magnetic). 



But this is by no means the only one of the kind. If we look 

 across the river from the bridge to the escarpment at the base of 

 the bridge pier on the Leigh side, we may see a Dyke filled in with 

 New Ked Sandstone : though small, it is plainly seen on the cut 

 face of the rock ; it has a course of about W. 17 S. by E. 17 !N"., 

 cutting obliquely across the beds and nearly along the strike. 

 The depth of this fissure, below the level of the present surface, 

 must be about 250 feet. Again, on the Clifton side, in the 

 roadway leading to the bridge, we may observe a number of these 

 veins from a few inches to two or three feet wide. Their general 

 course is N. 20 W by S. 20 E. (or magnetic K. and S). One we 

 may observe nearly at right angles to this direction, viz , E. 20 N., 

 and underlying at a smaller angle. The sides of the vein are 

 generally lined with calc spar, while the New Bed Sandstone fills 

 the central part of the fissure, showing that the fissure has been 

 open some time, a ad was getting gradually closed by crystalline 

 growth of calcic carbonate, before the sediments of the New E-ed 

 period had access to it. Strings of pure Haematite are sometimes 

 found in the centre of the veins. 



At the opposite end of the hill is another of these veins with a 

 N. and S. direction, it contains much crystallised Calcite and a 

 little New Red sediment. 



It will be observed that the character of these Dykes is much 

 like those, so ably described by Mr. W. Pengelly, 1<\E.S., on the 

 S. Devon coast near Berry Head : they are not so numerous with 



