NATURAL HISTORY OF MARL 487 



formed under existing conditions, but has been formed in some 

 previous time when conditions were not the same as now. (2) 

 The amount of dissolved salts is so small that the saturation 

 point is not approached until after the lakes are reached and the 

 slow evaporation and the reduction of the amount of dissolved 

 carbon dioxide in the water brings about deposition of the mineral 

 salts. (3) Some other cause, or causes, than the simple release 

 from the water of the solvent carbon dioxide must be sought. 



The first of these suggestions is met by the fact that marl is 

 found in lakes at and below the present level of the water, and 

 that it extends in most of them to, or even beyond, the very 

 edge of the marshes around the lakes, and over the bottom in 

 shallow parts of living lakes, even coating pebbles and living 

 shells. (2) The water of lakes with swift flowing and exten- 

 sive outlets, such as most of our marly lakes have, is changed 

 so rapidly that little if any concentration of a given volume of 

 water would occur while it was in the lake, and there is no 

 probability that any of the lakes visited by the writer have ever 

 been without an outlet. Indeed, many of them have outlets 

 which occupy valleys which have been the channels of much 

 larger streams than the present ones. Moreover, definite 

 measurements which, however, are subject to further investiga- 

 tion, have been made, which show that the volume of water 

 flowing out of these lakes is practically the same as that flowing 

 into them, i. e., the loss by evaporation is too small a factor to 

 be taken into account. Farther, recent investigations 1 have 

 shown that calcium, as the bicarbonate, is soluble to the extent of 

 238 parts in a million, in water containing no carbon dioxide. 

 As most of our natural waters, even from living clays, contain 

 no more than this amount of salt, even when they carry con- 

 siderable free carbon dioxide, and many analyses show a less 

 amount of it, the fact becomes plain that even if the carbon 

 dioxide were all lost there would be no precipitation from this 

 cause. (3) Considering these objections as valid it seems 



1 Treadwell and Reuter : Ueber die Loeslichkeit der Bikarbonate des Cal- 

 ciums und Magnesiums. Zeitschrift fiir Anorganish-Chemie, Vol. 17, 1898, p. 170. 



