Ch. XXIL] runn of cutch. 449 



thickness of the trias in the same region is estimated by Mr. Ormerod 

 at more than 1700 feet. Ripple-marked sandstones, and the footprints 

 of animals, before described, are observed at so many levels that we 

 may safely assume the whole area to have undergone a slow and grad- 

 ual depression during the formation of the Red Sandstone. The 

 evidence of such a movement, wholly independent of the presence of 

 salt itself, is very important in reference to the theory under considera- 

 tion. 



In the " Principles of Geology " (chap, xxvii.), I published a map, 

 furnished to me by the late Sir Alexander Burnes, of that singular flat 

 region called the Runn of Cutch, near the delta of the Indus, which is 

 7000 square miles in area, or equal in extent to about one-fourth of 

 Ireland. It is neither land nor sea, but is dry during a part of every 

 year, and again covered by salt water during the monsoons. Some 

 parts of it are liable, after long intervals, to be overflowed by river- 

 water. Its surface supports no grass, but is encrusted over, here and 

 there, by a layer of salt, about an inch in depth, caused by the evapora- 

 tion of sea-water. Certain tracts have been converted into dry land 

 by upheaval during earthquakes since the commencement of the pres- 

 ent century, and, in other directions, the boundaries of the Runn have 

 been enlarged by subsidence. That successive layers of salt might bo 

 thrown down, one upon the other, over thousands of square miles, in 

 such a region, is undeniable. The supply of brine from the ocean would 

 be as inexhaustible as the supply of heat from the sun to cause evapora- 

 tion. The only assumption required to enable us to explain a great 

 thickness of salt in such an area is, the continuance, for an indefinite 

 period, of a subsiding movement, the country preserving all the time 

 a general approach to horizontality. Pure salt could only be formed 

 in the central parts of basins, where no sand could be drifted by the 

 wind, or sediment be brought bv currents. Should the sinking; of 

 the ground be accelerated, so as to let in the sea freely, and deepen 

 the water, a temporary suspension of the precipitation of salt would 

 be the only result. On the other hand, if the area should dry up. 

 ripple-marked sands and the footprints of animals might be formed, 

 where salt had previously accumulated. According to this view, the 

 thickness of the salt, as well as of the accompanying beds of mud and 

 sand, becomes a mere question of time, or requires simply a repetition 

 of similar operations. 



Mr. Hugh Miller, in an able discussion of this question, refers to Dr. 

 Frederick Parrot's account, in his journey to Ararat (1836), of the salt 

 lakes of Asia. Id several of these lakes west of the river Manech, 

 " the water, during the hottest season of the year, is covered on its 

 surface with a crust of salt nearly an inch thick, which is collected with 

 shovels into boats. The crystallization of the salt is effected by rapid 

 evaporation from the sun's heat and the supersaturation of the water 

 with muriate of soda ; the lake being so shallow that the little boats 

 trail on the bottom and leave a furrow behind them, so that the lake 

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