6o The Ottawa Naturalist. [Ji 



very largely. Enquiries are frequently made as to the es 



Sources of in- istence of these deposits, and in order to pre- 

 formation ^ . ,., -iir i-<- 



re "marl Sent in SL readily accessible lorm such information as i.-^ 

 available from the published reports of the Geological Survey, 

 some of which are long out of print and others not convenient for 

 reference, the present paper has been prepared. While it is not 

 maintained that the subject has been exhaustively treated, since 

 the information relative to the occurrence of this substance in- 

 creases from year to year as the scope of the Survey's operations 

 is extended, the present paper will incorporate all available infor- 

 mation on the subject in regard to its occurrence in the provinces 

 of Ontario, Quebec, New Brunswick and Nova Scotia, taken 

 from the published reports of the Geological Survey and from 

 other sources of information, brought down to the present time. 

 Fresh-water marl occurs usually in marshes and shallow 

 lakes, and generally contains the shells of several species of fresh- 

 water mollusks. In the Geology of Canada, 1863, a good descrip- 

 Mode otoccu- tion of the mode of occurence and physical characters 



origfti ' of this material is given, which may be here quoted. 

 " Although belonging to the present geological period, this marl 

 is not always of recent formation ; inasmuch as the beds of it are 

 sometimes overlaid by peat, or by a soil supporting a growth of 

 large trees. At other times however, the marl covers the bottom 

 of shallow lakes or ponds, and is evidently in the process of depo- 

 sition. It appears to be formed by the waters of springs highly 

 charged with lime, which is at first held in solution as bicarbonate 

 but is deposited when these waters come to the air. It is thus 

 similar in its origin to the deposits of calcareous tufa, which occur 

 in many places where such calcareous springs flow over earth, 

 rocks and vegetation, instead of falling into lakes or marshes. 

 The presence of carbonate of lime is a necessary condition of the 

 development of shells, and various species of mollusca abound in 

 such waters. These by their remains, which often form a con- 

 sidrable portion of the deposits, give to them the name of shell- 

 marl, which is frequently applied. This substance is white and 

 earthy in its aspect, and, unless mingled with clay, is a nearly 

 pure carbonate of lime, which from its finely divided state is well 

 adapted to serve as ^ dressing for such soils as are deficient in 



