224 Capt. Hutton's Geological Report. [No. 111. 



While this deposit was precipitating from the changing waters of the lake, 

 the streams from the snows were bringing in large quantities of fine allu- 

 vial particles, such as sands and clays, and water-worn stones of various size. 



These were deposited above the gypsum of the lower end of the valley, and 

 passing on after that had ceased, reached to the upper end of Spiti. This 

 too, is seen to be the fact, for the beds of clay are found not only covering 

 the gypsum to a great depth, but also occupying its place at the upper ex- 

 tremity of the district. 



At the same time, the waters carried onwards an uniform solution of 

 clays, which they precipitated throughout the valley, the heavier stones 

 and boulders were forming beds at the points where the streams fell into 

 the lake. A reference to the annexed section will show the order and dis- 

 position of the various deposits which this valley contains, and serve to 

 illustrate the foregoing remarks : — 



(See plate) Fig. 8. 

 Section of the Spiti Valley. 



Let 3. 3. represent the fall or present line of descent of the river Spiti 

 from Leedung 12,037 feet, to Chungo 9897 feet above the sea. 



It will be at once apparent that the waters of the lake must have had 

 an increasing depth towards the lower end of the district, and that they 

 were fresh about A ; — brackish about B ; — and salt at C. The gypsum was 

 therefore deposited at the lower end, and is represented as lying within 

 the triangle 2. 2. 3. 



At the same time, above this marine formation a thick stratum of alluvial 

 deposits took place, forming a fresh water formation throughout the valley, 

 as represented within 1.1. 2. 2. 



The height at 1. on the left hand is 12,037 feet at the village of Leedung, 

 and the corresponding elevation at 1. on the right hand is the height of the 

 aqueous deposit about Chungreezing above Chungo, which is also 12,037 

 feet, thus beautifully exhibiting the line of the former surface of the 

 alluvium. 



Above this the waters rose and filled the valley, till they procured egress 

 at the lower end, beyond Leeo. 



Thus from the appearance of the district we gather, that it has once been 

 the bed of an extensive marine lake, whose waters having at length burst 

 through their barriers, have escaped by the channel of the Sutledge. 



This fact I consider to be indisputable, and it leads at once to a satis- 

 factory explanation of the origin of the deep alluvial deposits of clays, 



