OLD OCEAN COMMENCES WORK. 59 



illustrates, expels the carbonic acid in the form of a gas. 

 Under the high temperatures of the earliest periods, there- 

 fore, limestone could not exist. It has already been stated 

 that all the carbon, sulphur, and chlorine in existence must, 

 in those periods, have been represented by carbonic (CO 2 ), 

 sulphuric (SO 3 ), and chlorhydric (HC1) acids, existing in a 

 volatile state, mingled with the other gaseous constituents 

 of the atmosphere. At the same time, all the silica of the 

 globe, playing the part of an acid, would unite with the 

 fixed elements, producing silicates of complex constitution 

 — just such silicates as we actually find entering into the 

 structure of the oldest portions of the earth's crust. The 

 first rains which descended would be charged with the at- 

 mospheric acids just mentioned, which, attacking the solid 

 silicates at a high temperature, would, as the analytical 

 chemist knows, produce reactions resulting in the chlorids 

 of calcium (CICa), magnesium (ClMg),and sodium (CUSTa), 

 mingled with the sulphates of these bases (S0 3 KO, 

 S0 3 NaO, S0 3 CaO, S0 3 MgO). The liberated silica (Si 2 3 ) 

 would separate, and would be chemically precipitated dur- 

 ing the subsequent cooling of the waters, and would thus 

 give rise to the enormous beds of quartz which w T e actually 

 find among the very oldest strata, but nowhere else. 



Among the other silicates originally formed is a family 

 of minerals known as feldspars — very abundant, and con- 

 taining, besides alumina, large percentages of either potash, 

 soda, lime, or lithia, or two of these alkalies together. The 

 decomposition of these feldspars — especially orthoclase, or 

 potash-feldspar (Si 2 3 Al 2 3 KO) — must have taken place on 

 an extensive scale. The result would be a clayey hydrate, 

 called kaolin (Si 2 3 Al 2 3 ) when pure, which became the 

 basis of many clays and other argillaceous rocks like graph- 

 ic and roofing slates. The remainder of the orthoclase 

 would be in the form of silicates of potash (Si 2 3 K0) and 



