494 CHARLES A. DAVIS 



produced by the breaking and grinding up of fragments is held 

 in suspension for a longer or shorter time, carried about by cur- 

 rents, and finally sinks to the bottom in the quieter and deeper 

 parts of the lakes. 



Chara may also be looked upon as an important agent in 

 giving the peculiar distribution to marl which has been noticed 

 by every one who has "prospected" beds of material. The fact 

 is frequently noticed that beds of several, and even as much as 

 twenty or more, feet in thickness will "run out" abruptly into 

 beds of "muck," or pure vegetable debris, of equal thickness. 

 This distribution may show that up to a certain time conditions 

 unfavorable to the growth of Chara are favorable to other plants 

 obtained, until a depth of water was reached at which Chara was 

 able to occupy the bed of muck, covering it from the bottom up, 

 and holding the steep slope of the muck in place by mechanically 

 binding it there by its stems and the root-like bodies by which 

 it is connected with the mud. From the time when the Chara 

 began its occupation of the muck the amount of organic matter 

 left would decrease, and the amount of calcareous deposit would 

 increase, until the latter predominated. The disturbing factors 

 of currents and waves can be disregarded, for these abrupt 

 unions of marl and muck are found, so far as the observa- 

 tions of the writer go, in most sheltered places, and not where 

 either currents or waves could ever have operated with any force 

 or effectiveness. Moreover, in a lake where the marl is evi- 

 dently now actively extending, the slope was observed to be 

 nearly perpendicular, and the steep banks thus formed were 

 thickly covered with growing Chara, to the exclusion of other 

 large forms of plant life, and the lower parts of the growing 

 stems were buried in mud which was mainly pure marl. 



In regard to the species of Chara which seems to be the 

 active agent in precipitation in the lakes of central Michigan, it 

 is the form commonly known as CJiara fragilis, but it is probable 

 that careful study of the species throughout the range of the 

 marl will reveal, not a single form, but a number of allied spe- 

 cies, engaged in the same work. It may be well to suggest that 



