194 HALL AND SARDESON — THE MAGNESIAN SERIES. 



Coiwposition of spring and other Waters. — Attention has already been 

 directed to the existing conditions of continental drainage. The present 

 rainfall throughout the area of the Magnesian series will average about 

 30 inches per annum. If one-third of this, as meteorologists estimate, 

 soaks into the ground, there is an enormous percolation. This water may 

 not all pass through the rocks under discussion, but that much of it does 

 is proved by the many springs issuing from the rocks throughout their 

 entire extent. The composition of these spring waters, together with 

 those of a few springs from the glacial drift, without any positive proof 

 that they come in contact with other carbonate masses than the pebbles 

 lying among the drift debris, may be thus summarized : 



1. An average of seven mineral springs of Wisconsin gives in grains per gallon, 

 CaCOs, 12.640 ; MgOO.,, 8.981. 



2. An average of seven mineral springs of Minnesota gives in grains per gallon, 

 CaCOa, 9.250; MgCOg, 4.043. 



3. An average of six artesian wells of Iowa gives in grains per gallon, CaCOg, 

 13.085; MgCO.,, 5.678. 



4. An average of four lakes and rivers in Minnesota gives in j^rains jjer gallon, 

 CaCOs, 6.102; MgCOg, 3.332. 



It will be seen from the above figures that, gathered from every con- 

 dition of occurrence, the natural waters of the region underlain by the 

 Magnesian series are yielding a greater proportion of calcium carbonate 

 than of magnesium carbonate. 



Analyses of Travertine and impure Coral. — Again, taking into considera- 

 tion the deposits from these waters, the results are even more marked. 

 Ver}^ often travertine is deposited. Mr C. P. Berkey, of the University of 

 Minnesota, analyzed two specimens — one deposited by waters discharged 

 from Trenton limestone at Minneapolis, Minnesota, with Trenton shales 

 and glacial drift debris above ; the other discharged from Saint Law- 

 rence dolomitic shales at Osceola, Wisconsin, with Jordan sandstone, 

 Oneota dolomite and glacial drift above — with this result : 



Minneapolis travertine. Osceola travertine. 



CaCOg 98.01 per cent. 98.20 per cent. 



MgCOg 1.44 " 1.75 



99.45 '' 99.95 " 



There is no reason to suppose that the solvent power of water is any 

 different now than it has been in any geologic period since the Paleozoic 

 era. The inevitable result of such solvent action is to reduce the pro- 

 portion of CaCOg remaining in the rocks constantly toward that found in 

 normal dolomite. That the condition of a normal dolomite has not yet 

 been reached may legitimately be inferred from the chemical composi- 

 tion of the solid contents of the waters, as shown in the figures above ; it 



