Correspondence — Mr. J. R. Bakyns. bll6 



of a glacier is declining, it becomes in its lower course only 

 a transporting, not an eroding agent, and this would facilitate for 

 a time irregular erosion. Professor Davis discusses the origin of 

 Corrie Basins, and concludes with a review of previous writings on 

 the subject of glacial erosion. This and the previously mentioned 

 paper are illustrated by excellent photographic plates. 



Professor Davis gives a graphic account of a fault scarp in the 

 Lepini Mountains of Italy (Bull. Geol. Soc. Amer., vol. xi, April, 

 1900). The region, as described by Signer Viola, consists of 

 Cretaceous limestone, capped here and there with Eocene beds, 

 uplifted and separated from the Eocene of the Sacco Valley by 

 a fault of considerable magnitude. Extinct Quaternary volcanoes 

 occur on the southei'n part of the fault line. The fault scarp may 

 be seen from Morolo station to occur along the mountain base. If 

 the original uplift of the mountain mass ever produced a great fault 

 cliff all traces of it are now destroyed, for the front is carved into 

 a succession of buttressing-spurs and ravines. ' Eock-fans ' or 

 debris due to the retrogression of the escarpment are described. 

 The fault scarp, in Professor Davis' opinion, is much more recent 

 than the great dislocation which upraised the mass of the mountain 

 front, and was probably due rather to an irregular depression of the 

 Piedmont Eocene mass than to a further elevation of the Cretaceous 

 mountain block. 



In an article on the Fresh-water Tertiary Formations of the 

 Eocky Mountain Eegion (Proc. Amer. Acad., vol. xxxv, March, 

 1900), Professor Davis maintains that sufficient attention has not 

 been given to the fact that rivers deposit as well as erode, and that 

 in consequence the probable fluviatile origin of most Piedmont 

 plains has not been generally realized. He gives reasons for 

 believing that mere continuity of even-bedded deposits, such as 

 occur in the Tertiary formations of Western America, even if 

 occiipying many square miles, should not alone be taken as con- 

 clusive evidence of lacustrine origin. The object of his paper is to 

 promote consideration of the subject. 



C0I^I^ESI30lf^z^:E:l^^CE. 



A FELSTONE DYKE ON LLECHOG. 



Sir, — In my paper published in the Geological Magazine under 

 the title " Firstfruits of a Geological Examination of Snowdon,"^ 

 I said that the Felstone Dyke on Llechog might possibly be the 

 same as are seen in Cwm Clogwyn at the foot of Llechog. I have 

 now satisfied myself that such is the case, and I give a diagram (not 

 drawn to scale) showing how the dyke rises through the cleaved 

 felsitic rocks of the mountain, and a sketch - map of the area 

 where it occurs. The dyke is from 15 to 20 yards wide where 



1 Geol. Mag., 1900, June, p. 267. 



