Posted on Friday 31 October 2008
also slimy and fetid to the last degree, its taste being accuratelydescribed as half brine, half rancid oil. Indeed, the salt has been sofar precipitated already that there is now five times as much chlorideof magnesium left in the water as there is common salt. By the way, itis a lucky thing for us that these various soluble minerals are of suchconstitution as to be thrown down separately at different stages ofconcentration in the evaporating liquid; for, if it were otherwise, theywould all get deposited together, and we should find on all old saltlake beds only a mixed layer of gypsum, salt, and other chlorides andsulphates, absolutely useless for any practical human purpose. In thatcase, we should be entirely dependent upon marine salt pans andartificial processes for our entire salt supply. As it is, we find thematerials deposited one above another in regular layers; first, thegypsum at the bottom; then the rock-salt; and last of all, on top, themore soluble mineral constituents.
The Great Salt Lake of Utah, sacred to the memory of Brigham Young,gives us an example of a modern saline sheet of very different origin,since it is in fact not a branch of the sea at all, but a mere shrunkenremnant of a very large fresh-water lake system, like that of thestill-existing St. Lawrence chain. Once upon a time, American geologistssay, a huge sheet of water, for which they have even invented adefinite name, Lake Bonneville, occupied a far larger valley among theoutliers of the Rocky Mountains, measuring 300 miles in one direction by180 miles in the other. Beside this primitive Superior lay a secondgreat sheet–an early Huron–(Lake Lahontan, the geologists call it)almost as big, and equally of fresh water. By-and-by–the precise datesare necessarily indefinite–some change in the rainfall, unregistered byany contemporary ‘New York Herald,’ made the waters of these big lakesshrink and evaporate. Lake Lahontan shrank away like Alice inWonderland, till there was absolutely nothing left of it; LakeBonneville shrank till it attained the diminished size of the existingGreat Salt Lake. Terrace after terrace, running in long parallel lineson the sides of the Wahsatch Mountains around, mark the various levelsat which it rested for awhile on its gradual downward course. It isstill falling indeed; and the plain around is being gradually uncovered,forming the white salt-encrusted shore with which all visitors to theMormon city are so familiar.
But why should the water have become briny? Why should the evaporationof an old Superior produce at last a Great Salt Lake? Well, there is asmall quantity of salt in solution even in the freshest of lakes andponds, brought down to them by the streams or rivers; and, as the waterof the hypothetical Lake Bonneville slowly evaporated, the salt andother mineral constituents remained behind. Thus the solution grewconstantly more and more concentrated, till at the present day it isextremely saline. Professor Geikie (to whose works the present paper ismuch indebted) found that he floated on the water in spite of himself;and the under sides of the steps at the bathing-places are all encrustedwith short stalactites of salt, produced from the drip of the bathers as