﻿Nichols: The vegetation of Connecticut 195 



erence has yet been made, namely, the formation of marl. Marl 

 deposits are always associated with calcareous regions, and in 

 Connecticut are confined to the limestone areas in the western 

 part of the state. At Twin Lakes, Salisbury, there are quite exten- 

 sive deposits, estimated in places to exceed a hundred feet in depth, 

 and there are similar deposits near Danbury and elsewhere. Chem- 

 ically, pure marl contains about ninety-five per cent, of calcium 

 carbonate. Formerly such deposits were supposed either to rep- 

 resent shell remains, or else to have originated through mechanical 

 sedimentation or chemical precipitation from calcium-containing 

 waters.* But while the presence in marl beds of Chara and other 

 plant "fossils" had frequently caused comment, and although it 

 is a common observation that in lakes where marl is being de- 

 posited, submersed aquatic plants are usually coated with a thin 

 crust of calcium carbonate, it remained for Davisf to demonstrate 

 the important role played by plants, particularly by the alga 

 Chara, in marl formation. 



In a general way it may be asserted that plants are 

 able to bring about the formation of marl by causing the 

 precipitation of various calcium salts which may occur dis- 

 solved in the waters of lakes and ponds. Two methods by which 

 plants may effect this result are easily conceived, (i) The ab- 

 straction of carbon dioxide from water in which calcium is present 

 in excess, held in solution by free carbon dioxide, would cause the 

 precipitation of the calcium salts. (2) The combination of the 

 oxygen liberated by plants with easily soluble salts like calcium 

 bicarbonate, thereby converting them into less soluble salts like 

 calcium carbonate, would result in precipitation. The existence 

 of still a third, and possibly even more effective, method of calcium 

 concentration has been pretty conclusively demonstrated by Davis 

 in the case of Chara. (3) The calcium accumulates in the cells of 

 this plant in the form of calcium succinate, one of the few water- 

 soluble salts of calcium. Later on, although just how is not as yet 

 wholly understood, the dissolved salts are excreted and deposited in 



