﻿vol. 64.] soltjtion-y alleys in the glyme aeea. 343 



Discussion. 



M. M. Allokge, who stated that he had been over a part of the 

 ground with the Author, commented on the very few traces of 

 mechanical erosion visible over the Great Oolite plateau, on the 

 number of dry valleys, and especially on the occurrence of reversed 

 grades in the thalwegs of some, which he attributed to chemical 

 solution. They reminded him of the Carboniferous-Limestone regions 

 and the cul-de-sac valleys or kesselthiiler of the Karat in Istria, 

 where underground solution was undoubtedly the controlling factor 

 of the topography. He thought that the features in the district 

 described could only be adequately portrayed by a model, owing to 

 the thin character of the limestone and the climatic conditions. He 

 considered that solution had acted by a gradual melting-down of the 

 limestone, not by unroofing subterranean channels. He thought that 

 one of the most interesting results of the Author's investigations was 

 the explanation suggested for the ' misfit rivers ' of the district. 



Mr. E. A. Martin welcomed the paper. He thought that it 

 contained a partial solution of the question of the origin of the 

 Eubble-Drift and dry Chalk- valleys, which had been attributed by 

 Mr. Clement Eeid to other causes. The speaker had for a long 

 time doubted the efiicacy of Mr. Eeid's theory of a frozen soil, and 

 thought that in ' solution-valleys ' there was possibly a better ex- 

 planation. He did not, however, wish to attribute too much to the 

 solution-theory. Wherever there was running water, there must, 

 of course, have been a certain amount of erosion ; but the two 

 together, solution and erosion, went hand-in-hand to excavate the 

 Chalk-valleys. 



Mr. H. B. WooDAVABD dissented from the Author's explanation 

 of the Glyme valleys. The Great Oolite contained bands of marl 

 or clay, especially in the lower portions ; springs were given out 

 at different horizons ; and there were no signs of dislocation in 

 the quarries to indicate subsidence. Moreover, there was much 

 evidence of mechanical erosion in the clay brought down by the 

 streams, notably in the lake in Glympton Park, the mud from 

 which was being dredged when he visited the area. All the facts 

 tended to show that the valleys were eroded by ordinary chemical 

 and mechanical processes. 



Mr. G. ^Y. Young was glad to hear that the Author considered 

 that the dry valleys of the Chalk were also due to solution, as 

 it supported the views advocated by the speaker in a paper read 

 before the Geologists' Association some three years previously. He 

 felt that, if the Author's view was correct in regard to these Jurassic 

 rocks, there was a still stronger case in regard to the Chalk, where 

 the plateau was protected by an impervious capping of clay, so that 

 the dissolving action of the rainfall was confined to the unprotected 

 valley-areas,which were thus gradually eaten deeper and deeper. 



Mr. W. Baldwin congratulated the Author upon the interest of 

 his paper, and readily accepted the theory of solution- valleys in the 

 Mountain Limestone, where caverns had been unroofed. He had 

 examined the valley near Box Hill, in Surrey, one of those mentioned 



