29 



(5-) Lane, A. C. Notes on the origin of Michigan bog 

 limes. Vol. X, pt. 3, Reports Michigan Geological Survey, pp. 

 199-223. 



Disregarding tlu- points in controversy, which are of no par- 

 ticular practical importance, it may be said that marls are de- 

 posited in hikes by spring or stream waters carrying lime car- 

 bonate in solution. The actual deposition is in part due to 

 purely physical and chemical causes, and in part to the direct 

 or indirect action of animal or vegetable life. The result, in 

 any case, is that a calcareous deposit forms along the sides and 

 over the bottom of the lake, this deposit consisting of lime car- 

 bonate, mostly in a finely granular form, interspersed with shells 

 and shell fragments. 



Geographic distribution of marl deposits. The geographic 

 distribution of marl deposits is intimately related to the geo- 

 logic history of the region in which they occur. MairNbeds are, 

 as indicated in the preceding section, the result of the filling of 

 lake basins. Lakes are: not common except in those portions 

 of the United States which were affected by glacial action, since 

 lakes are in general due to the damming of streams by glacial 

 material. Workable marl deposits, therefore, are almost ex- 

 clusively confined to those portions of the United States and 

 Canada lying north of the former southern limit of the glaciers. 



Marl beds are found in the New England States, where they 

 are seldom of important size, and in New York, where 

 large beds occur in the central and western portions of the 

 State. Deposits are frequent and important in Michigan, and 

 in the northern portions of Ohio, Indiana, and Illinois. Marl 

 beds occur in Wisconsin and Minnesota, but have not been as 

 yet exploited for cement manufacture. 



Composition. As show : n by the analyses below, marls are 

 usually very pure lime carbonates. They, therefore, require the 

 addition of considerable clay to bring them up to the proper 

 composition for at Portland cement mixture. 



The marls are readily excavated, but necessarily carry a large 

 percentage of water. The mixture, on this account, is com- 

 monly made in the wet way, which necessitates driving off a 

 high percentage of water in the kilns. Analyses of typical marls 

 and clays are given in the following table. 



