21$ HISTORY OF GEOLOGY AND PALEONTOLOGY. 



Chemical Geology^ and the later work of J. Roth (1879) con- 

 tains an even fuller account of this subject. The deposits 

 formed in a purely chemical way, without any assistance from 

 organisms, have been so systematically and ably elucidated by 

 Bischof and Roth, that there is now scarcely any difference of 

 opinion among geologists regarding the origin of calcareous 

 tufa, travertine, ochre, hydrous ferric oxide or " moorband pan," 

 siliceous sinter, fresh-water limestone and dolomite, and other 

 kinds of spring and fresh-water deposit. Mellard Reade has 

 more recently calculated the amount of material held in 

 chemical solution in rivers and transported by them to the sea. 

 If his figures are confirmed by further analyses, they will 

 form the basis of far-reaching conclusions. 



The earliest analyses of sea-water made in the nineteenth 

 century were those of Vogel, Marcet, Wollaston, and Bibra. 

 In the year 1845, the famous Copenhagen chemist, Forch- 

 hammer, began a series" of researches on the composition of 

 sea-water, and twenty years later his admirable treatise on 

 the subject was published. Bischof and Roth also investi- 

 gated the composition of sea-water. 



It may be said in general that no chemical deposits form on 

 the floor of the open sea, as the immense volume of sea-water 

 holds the substances in solution. Only very small quantities 

 of lime carbonate and magnesium carbonate or dolomite seem 

 to be deposited under certain conditions. 



In inland salt seas, gypsum and rock-salt separate out in 

 large quantities and form thick floor deposits for example, in 

 the Great Salt Lake of Utah, the salt seas of Central Asia and 

 Southern Russia, in the Shotts of the Sahara, and in many 

 bitter lakes. The process of the spontaneous evaporation of 

 sea-water was studied by Usiglio (1849) on Mediterranean 

 water, and by his laboratory experiments he determined the 

 order in which the various salts are deposited during progres- 

 sive concentration of the brine liquor. Usiglio's results were 

 then applied in the production of salt from sea-water for 

 commercial purposes. 



An attractive account of the saline basins in the North 

 Caspian Steppes was contributed to Erman's Journal by Baer 

 in 1854. The salt deposits were carefully described, and the 

 author concluded from the distribution of the basins that the 

 Caspian Sea was formerly of far wider extent. Baer demon- 

 strated that the waters of the Caspian Sea are still diminishing 



