634 THE FRESH-WATER LOCHS OF SCOTLAND 
traversed by subterranean waters communicating ultimately with the 
Green River, a tributary of the Ohio, by two deep springs. These 
waters are known by the following names : — The Dead Sea, 100 feet 
long, bordered by cliffs 60 feet in height ; the River Styx, a body of 
water 40 feet wide by 400 feet long ; Lake Lethe, a broad basin 
enclosed by a wall 90 feet high ; and Echo River, which is about 
three-quarters of a mile long, from 20 to 200 feet wide, and from 
10 to 40 feet deep. Whenever there is a flood in Green River, the 
streams in the cave become a continuous body of water. 
The fauna of the Mammoth Cave has been determined by Putnam 
and Packard^ and Cope, who have catalogued twenty-eight truly 
subterranean species, besides those that may be regarded as having 
migrated from the surface. Blind grasshoppers, blind crayflsh 
{^Camhariis pellucidus)^ blind fish {Amblyoj^sis spelccus) are found, and 
the great antiquity of the cave is shown by the fact than the true 
subterranean fauna may be regarded as chiefly of Pleistocene origin. 
Twin Lakes are situated in the southern part of Lake County, 
Colorado, on the west side of the valley of the Arkansas River, 
a tributary of the Mississippi, and are about 9200 feet above 
sea-level. They lie a short distance below the mouth of Lake Creek 
Canon, and the basins which they occupy were doubtless scooped out by 
the glacier which at one time flowed down this canon and joined that 
occupied by the Arkansas River. As the glacier receded, two terminal 
moraines were formed, one of which maintains the water in Lower 
Twin Lake, and the other the water in Upper Twin Lake. The lakes are 
entirely surrounded with morainal detritus^ with no bed-rock exposed 
except for a short distance along the northern shore of the lower lake. 
The area of the Upper Twin Lake at about midsummer is 474 acres, 
and that of the Lower Twin Lake 1440 acres. Hayden ^ in 1873 
gave the greatest depth as 79 feet in Upper Lake, and 76 feet in 
Lower Lake. Juday^ gives 82 feet and 74 feet for the Upper and 
Lower Lakes respectively ; but both size and depth are subject to 
variation, as the lakes are now used as a storage reservoir by the 
Twin Lakes Reservoir Company for irrigation purposes. A dam is now 
maintained in the old outlet, while the present outlet is a canal. 
The principal affluent is Lake Creek, which flows into the west end of 
Upper Lake from Lake Creek Canon. About a dozen other streams of 
various sizes contribute their supply of water to the lakes. 
The lakes, as might be expected from their altitude, have an alpine 
1 Packard and Putnam, Inhabitants of Mammoth Gave, 1872. 
2 See "Twin Lakes," ^?m. Rep. U.S. Geol. Surv. Territories for 1873, pp. 47 
and 54, 1874. 
^ See " A Study of Twin Lakes, Colorado, " Bull. Bureau of Fisheries, vol. xxvi. 
p. 152, Washington, 1907. 
