(horizontal lines in box) Lakes. (vertical lines in box) Bayirs. ] We may now return to a closer study of the largest of these formations, the great Kevir in Persia. This mud-lake, with a dry surface, measures 500 km. (310 miles) in length and 200 km. (124 miles) in width over its largest dimensions. Hedin estimates its area at 55,000 sq. km. (21,142 sq. miles) or the same as that of the great Lake Michigan on the boundary between the United States and Canada. Due to the continuous growth of the salt proportion through the inflow of Kevirs and through superficial evaporation a salt crust of varying thickness is formed near the surface of the lake. Hedin caused a hole to be cut with an iron bar. He first encountered a 10 cm. (3.9 in.) deep covering of clayey paste, and then the salt crust about 7 cm. (2.8 in.) thick resting on a semi-dry layer of clay with a depth of 15 cm. (5.9 in.). Farther below, softer strata of clay followed, becoming more watery the deeper he went. The iron bar carelessly wielded would have disappeared in the mire. Another investigator, Buhse, examined a piece of the crust, which when dry is fairly solid and of a yellowish-grey colour. One half consisted of sand (probably quartz-sand), one sixth of limestone, 6.1 per cent. oxide of iron (causing the yellow colour), 5.3 per cent. common salt, 2.5 per cent. sulphate of sodium, and 2.1 per cent. clay. Rain converts this surface layer into a plastic mass, which persistently sticks to the clothes of the traveller or to the bodies of the camels if they should slip and fall into the mud. Not the slightest trace of vegetation or of any life exists. On the shore of the mud-lake small flat elevations and depressions may be found; otherwise, the surface is as level as that of an ordinary lake.