1841.1 Capt Mutton's Geological Report. 223 



Those phenomena and appearances have already been stated, and it 

 therefore now only remains to show, that they are precisely in accordance 

 with the theory proposed, and prove it to be correct. 



When the vast ranges of the Himalya burst upward through the watery 

 shroud which had hitherto enclosed the earth, the lofty ridges which sur- 

 rounded the lake became at once the eternal reservoirs of everlasting snows, 

 from which numerous streams descended, as in the present day. 



The waters of the lake itself were salt, being taken from the ocean, and 

 they gradually yielded to the streams which descended from the heights, 

 until they became first bracMsh, and finally fresh. 



The largest body of water which was supplied from the snows was that 

 of the Spiti river, and to its current are partly attributable the appearances 

 of the present valley. 



Let us then look well to the mode of operation. 



The lake was salt or marine ; its waters after the agitation caused by the 

 upheavement had ceased became tranquil, and as their nature began imme- 

 diately to undergo a change from the influx of the snow streams, a deposit 

 from its waters commenced. That deposit I hold to be the bed of fri- 

 able or earthy gypsum. 



The reason why it occurs at the lower end of the lake is this : — The 

 downward rush of the Spiti waters from the heights of the Paralassa range, 

 caused a strong current to advance far onwards into the valley, where it 

 became less and less rapid, till it died away, or was checked by the body 

 of water below. 



Thus we may at once perceive, that while the fresh waters usurped the 

 upper portion of the valley, the middle and lower parts were occupied 

 by brackish and salt waters respectively — a circumstance that may be fully 

 understood by observing the confluence of a large river with a gulf or 

 any part of the sea. The river is fresh, the junction brackish, and the 

 ocean salt. 



The gypsum or sulphate of lime would therefore naturally be pre- 

 cipitated in the greatest quantities at the lower end of the valley, where 

 the waters were the saltest, and the bed would gradually become thinner 

 as it advanced into the intermediate part where the lake was brackish, and 

 it would be wanting altogether in the upper part where the waters were 

 fresh. This is precisely the fact, for the upper end or head of the Spiti val- 

 ley is free from the gypseous deposit, while towards the middle we find the 

 rocks often incrusted with it, or forming with fragments of shale and other 

 rocks a gypseous breccia, which becomes less crystalline as it advances to the 

 lower end of the district, where it yields to the thick beds or deposit of 

 friable gypsum. 



2e 



