﻿Correspondence — Mr. A. J. Jukes Browne. 477 



assign to the Upware rock is, I think, so worded as to convey a 

 wrong impression. " He correlates it with the lowest portion of the 

 Corallian region, on account of its containing Cidaris florigemma, a 

 reason which would make us assign to it nearly the highest." This, 

 coupled with the rest of the paragraph, and their use of the word 

 Corallian, would give rise, I think, to the supposition that I had. 

 placed the Upware rock below the Coral Eag. On the contrary, I 

 take some pains to prove it to be Coral Eag, and the only support 

 for this statement is that, as I was contending against Mr. Seeley's 

 attempt to place the bed in the Kimmeridge series, and as G. flori- 

 gemma was then supposed to characterize rather the lower part of 

 the Coral Eag, I point out that the atfinities of the Upware rock are 

 downward rather than upward, so that it cannot even be paralleled 

 with the Continental Sequanien. It is true that, according to Messrs. 

 Blake and Hudleston, the position of the zone of G. florigemma is 

 less constant than it was supposed to be ; but in reasoning on that 

 point, I used the best information to be obtained at the time, and the 

 change does not materially weaken my main position that the 

 Upware limestone is true Coral Eag, as the word was then under- 

 stood. 



St. John's College, Cambridge. T. G. Bonnet. 



THE ORIGIN OF CIRQUES. 



SiK, — In a recent number of the GtEologioal Magazine (p. 273), 

 Mr. Bonney has replied to the arguments adduced by Mr. Helland 

 in favour of the glacial origin of cirques (Quart. Journ. Geol. Soc, 

 vol. xxxiii. p. 142), and has adduced many cogent reasons in support 

 of the explanation he has previously given, viz. " that the cirques 

 are mainly produced^ by the combined erosive action of streamlets." 



May I be allowed to cite what I conceive to be an illustrative case, 

 occurring in a country which I have lately visited, and where it 

 would be difficult to discover any traces of ice action, but where the 

 erosive power of torrential rains is markedly exhibited ? I refer to 

 Upper Egypt, and especially to that district lying between the valley 

 of the Nile and the Eed Sea. 



The eastern bank of the Nile above Cairo is bordered by a desert 

 plain, about three or four miles wide, and stretching up to the high 

 cliffs beyond, which rise into mountains some 600 or 700 feet high, 

 and form the range known as the Arabian chain. These cliffs are 

 furrowed by numerous deep gorges and valleys opening on to the 

 desert plain below, over which is spread out the detritus brought 

 down from the hills ; for Egypt is not the rainless country it is 

 sometimes represented to be, and in winter-time rain falls occasion- 

 ally in quantity sufficient to convert these dry valleys into rushing 

 torrents ; thus among the recesses of the bare and barren limestone 

 rocks, into which the valleys lead, signs of water-action are every- 

 where visible. A cirque in such a land as this could hardly be 

 formed by any other agency than that to which Mr. Bonney attributes 

 them, and yet a very cirque-like hollow came under my notice while 

 exploring one of these ravines. I had ridden some distance along 



