216 Capt. HuttovUs Geological Report QNo. 111. 



with slight interruption, the transition or lowest secondary series con- 

 taining fossil exuviae of marine Mollusca. 



From the point of junction of the Spiti and Sutledge to the head of 

 the Spiti valley, we find every thing indicating the former presence of 

 an extensive lake. These indications consist in beds of friable or earthy 

 gypsum, clays, sand, and rolled pebbles now left high in horizontal strata 

 above the course of the river at the present day. 



These accumulation^ are also seen to be the thickest and most extensive 

 at the lower end of the valley, where the mountains form recesses, and 

 where the slope is the most gradual. We find the gypseous beds alone at 

 the lower end, and we also find them growing thinner and dying out as 

 they approach the higher and narrower part of the valley, until at last 

 their presence is only to be traced in the incrustations of other rocks. 



The clays and sands which have been deposited upon these beds are, on 

 the other hand, universal throughout the valley wherever they could 

 find a resting place, and they pass on after the gypsum has ceased up to the 

 higher portion of Spiti, where at length they yield to pebbles and boulders. 



I have called attention to these facts, because I shall presently show by 

 what means such an arrangement has taken place. 



It will, however, first be necessary to state the theory which these ap- 

 pearances suggest, and then to show how the phenomena presented to our 

 view, are in accordance with that theory. 



Theory of the Spiti Valley. 



We have already seen that the valley bears every appearance of having 

 been at some remote period the bed of an extensive lake, which at length, 

 by the accumulations of its waters, and its enormous pressure upon the 

 rocky barriers which confined it at the lower extremity of the valley, burst 

 forth with irresistible power and devastating effects down into the district 

 of Kunawur. I shall endeavour to trace in detail the circumstances which 

 may have led to this outburst of the Spiti waters. 



The first formation of such a lake may have occurred from one of three 

 distinct causes, namely : — 



First. If we allow the existence of these vast mountains previous to the 

 flood, the lake may have accumulated in the bosom of the valley from the 

 melting of antediluvian snows, and thus, (suppossing the Mosaic narrative 

 to be correct,) it will be seen, that although originally composed of fresh 

 waters, it must have changed its nature and become salt at the period of 

 its submersion by the deluge ; and again in after years, when that deluge 



