326 Reports and Proceedings — 



A special plienomenon was described as now and then occurring in the alluvium, 

 namely, a sloping of the alluvial strata, looking at first like false-bedding on a large 

 scale ; and, further, a curving or bending of them, till they reached round even 

 beyond the perpendicular. This the author attributed to the ploughing of the foot 

 of a glacier against the alluvium that had been formed in front of it by its own 

 streams. 



The last class of alluvial deposits would be tlie lacustrine-, but a description of these 

 was reserved for a future portion^of the paper. 



Summary and Inferences. — There was evidence of a succession of three states : — 

 1st. The cutting of the valleys. 2nd. The accumulation of alluvial matter. 3rd. 

 The cutting down of the streams through that alluvial matter. 



Accumulation denotes an excess of supply of material from the 'rocks (by disin- 

 tegration) over what can be carried away by the streams. 



Denudation, or the cutting down of the streams through their alluvium (the 

 lowering of their beds), denotes a deficiency of supply of material from the rocks as 

 compared with the transporting power of the streams. Hence the author inferred 

 that the period of great accumulation of these alluvial deposits was one of great 

 disintegration of rocks, one of intense frost; in other words, it was the Glacial 

 period, and that the denudation occurred when the cold lessened, and there came to 

 be a smaller supply of disintegrated material. 



The connexion of various glacial phenomena with the alluvium, such as the one 

 described above, was taken to corroborate the inference that the greater deposits 

 were made during the Glacial epoch. 



Discussion. — Mr. Sowerby confirmed the observationsiof the author, and said that 

 the phenomena described by him are not confined to the valley of the Indus, but that 

 they occur in other parts of India. 



Mr. Blanford remarked that the peculiarity of the region of High Asia is the 

 enormous amount «f alluvial deposits— enormous both as regards their thickness and 

 the area they occupy. This peculiarity is rendered the more striking as the deposits 

 are not concealed by vegetation. He remarked upon the absence of stratification in 

 the fan-shaped and other deposits, and at the mouths of streams. He expressed 

 himself not quite satisfied that glaciers were the cause of the contorted beds referred 

 to by Mr. Drew. The accumulation of great masses of deposits 700 — 800 feet thick 

 he thought was frequently due to landslips, and he stated that he had seen such 

 extending to 200 feet in thickness. 



Mr. Clifton Ward stated that he had frequently found it difficult to distinguish the 

 deposits at the mouth of streams from true alluvial beds. 



The Chairman remarked that the phenomena described by Mr. Drew were to be 

 observed elsewhere than in the district where his observations had been made, and 

 referred to examples both in this country and on the continent of Europe. 



Mr. Drew briefly replied. 



(4).— June 11, 1873.— Pro£ Bamsay, F.E.S., Vice-President, in the Chair.— The 

 following communications were read: — 1. " On thelfature and probable Origin of 

 the superficial Deposits in the Valleys and Deserts of Central Persia." By W. T. 

 Blanford, Esq., F.G.S. 



In this paper the author described the general characters of fte superficial deposits 

 of Central Persia, and noticed the physical geography and rainfall of that country. 

 He described especially the desert plains of the interior of the country, the paucity 

 and scantiness of the streams, most of which terminate in salt swamps and lakes, 

 and the occurrence of vast slopes of gravel on the margins of the desert plains, 

 covering up the junction of the latter with the surrounding mountains. The desert 

 plains he regarded as in general the beds of ancient lakes. His general results may 

 be summed up as follows: — Persia has undergone a gradual change from a moister 

 to a drier climate simultaneously with the elevation of portions of its surface, result- 

 ing first in the conversion of old river-valleys into inclosed basins containing large 

 lakes, probably brackish or salt. Then, as the rainfall diminished, the lakes gradually 

 dried up, leaving desert plains. The amount of subaerial disintegration among the 

 rocks of the high ground he considered to be in excess of the force available for its 

 removal, the water which now falls only sufficing to wash the loosened materials from 

 the steeper slopes into the valleys, and hence the valleys in the upper parts are 

 gradually being filled up with coarse gravel-like detritus, just as their lower portions 

 have been already hidden beneath lake-deposits. 



Discussion. — Mr. Prestwich could hardily understand how, without a very close ex- 

 amination, it could be ascertained that there were no outlets from the plains which 

 had been mentioned. If by any possibility there were such outlets, great difficulty 

 would arise in accepting the theory. He was not quite satisfied as to the evidence of 

 the thickness of the deposits on the slopes, and inquired as to the presence of organic 

 remains. 



