332 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [March 22, 



without forming any surface-course whatever. Supposing that a 

 stream was to run from e towards h, there cannot be any doubt 

 that it would cut a ravine course, would fill up the depression at d, 

 and, in passing down the steep slope from c to h, would soon cut 

 deeply into the part at c, and, in no long period, produce an 

 evenly-inclined channel for the whole of the distance. There is, how- 

 ever, not the least trace of such an action having ever occurred. 

 The sides of the lower valley pass gradually round at the upper end, 

 vrithout any such irregularity ; and, I think, no one examining the 

 valley itself could come to any other conclusion, than that it had 

 been excavated by the same agent which denuded the district, and 

 cut away the whole mass of the Tabular Hills to the north and east 

 of their main escarpment. 



Now, if a brook had run down this part of the valley, formed a 

 gradually-sloping channel, and reduced it to the same state as that 

 where one does run ; if it had removed the whole of the detritus, 

 and given the valley the form of 8ect. 1, fig. 2, there would have been 

 no certain evidence whatever to indicate or prove that the whole had 

 not been excavated by it. As it is, however, we must conclude that 

 nearly the whole was due to a cause acting before there was any such 

 surface-drainage, and that the brook has merely cut away some of 

 the detritus left in the valley, which had not been entirely removed 

 by the denuding agent. Though I am far from inferring that such 

 has always been the case, for each particular district ought to be 

 judged of from the facts there seen, and not by any a 'priori reason- 

 ing, yet I cannot but observe that we are thus led to form this con- 

 clusion for valleys whose form is very much more than ordinarily in 

 accordance with what would be due to the long-continued action of 

 such streams. I might easily fortify this deduction by reference to 

 the phsenomena observed in other valleys in the neighbourhood, but 

 will not, for fear of being tedious. 



If, then, these valleys in the Tabular Hills were excavated by the 

 same cause that denuded the district, it will be well to examine the 

 facts that may lead to a satisfactory conclusion, with respect to what 

 that agent was. As previously mentioned, the general line of these 

 valleys, in the part under consideration, is north-north-west, being 

 nearly in the line of dip ; there being others of a different character 

 at right angles to that direction. Though, in the case of Yedman- 

 dale, there is no very decided evidence of any considerable fault, yet 

 I think there is good reason to beheve that it and the other valleys 

 are along the lines of this or some other structural weakness. 



The deltoid accumulations of detritus in Yedmandale, and the 

 nature of the rock of which it is composed, clearly indicate that it 

 was deposited by a current from the north-north-east. If these 

 valleys were excavated by the denuding agent, we must suppose that 

 the whole surface was submerged. If so, the above fact would prove 

 that there then was a considerable current from the north-north-east. 

 Supposing that a fault extended up the valley, becoming small or 

 ending in the top eastern branch, and that there was such a strong 

 north-north-east current, we must conclude that it cut away the 

 rock on each side of the fault, and gave rise to a ravine-shaped 

 valley, carr3nng away the detritus to the south into the vale of 



