NOTES Olf TRIAS DYKES. 165 



opinion of Professor Jukes, that the Avon gorge was at the time 

 it began to be formed the lowest part of the country, and 

 therefore may have been cut by the action of river-water. 



We further believe that the course of the Avon through the 

 gorge is in intimate connection with the systems of joints in the 

 Limestone, and that many of its bends are primarily due thereto. 

 The drainage would naturally begin to flow along the lines of 

 joints, and as these are mostly at right angles to each other, a 

 tortuous course would rise; when the drainage amounted to a 

 perennial stream, the angles where these break into one another 

 would get rounded off, and as the river gets older its origin would 

 get less plain. 



The direction of the joints in the Sea Wall quarry are as follows — 

 One set is N. 30 W. by S. 30 E., this corresponds with the main 

 direction of the reach between the Sea Wall and the round point ; 

 the other cuts these somewhat obliquely, being W. 15 IS. by 

 E. 15 S., this does not differ many degrees from the direction of 

 the reach under Cook's Folly. The reach also between the 

 St. Vincent's Rocks and Cumberland Easin again corresponds 

 in direction with that of the joints, being here about S. 20 E. by 

 1^. 20 W. If we may be allowed to reason back from this 

 coincidence, though we do not pretend that it establishes the point, 

 yet we may say it almost justifies the presumption that the gorge 

 owes its existence to the errosive and denuding action of water, 

 rather than to any cataclysmic throes or convulsions of nature, or 

 even faults which seem certainly absent as far as the direction or 

 course of the river is concerned. 



In conclusion we may mention similar Trias Dykes in 

 Carboniferous Limestone on the S. Wales coast. During a flying 

 visit to the Mumbles near Swansea, we noticed precisely similar 

 phenomena between Mumbles Head and Caswell Bay. 



At the corner of Langland Bay a small Dyke was observed 

 containing Haematite. The large artificial chasm near the Head 

 forming a notch in its outline, as seen from Swansea, is simply 

 one of these Trias Dykes which contained so much iron-ore, that it 



