ECKEL.] MARLS. 35 
geological reports issued by New York, Ohio, and other interior 
States. 
(2) In New Jersey and the States southward bordering on the Atlan- 
tic and Gulf of Mexico the term u marl" is commonly applied to 
deposits of soft, chalky, or unconsolidated limestone, often contain- 
ing considable clayey and phosphatic matter. These limestones are 
of marine origin and are not related to the fresh-water marl deposits 
here discussed. 
(3) In the same States mentioned in the last paragraph, but par- 
ticularly in New Jersey and Virginia, large deposits of the so-called 
"greensand marls" occur. This material is in no way related to the 
true marls, which are essentially lime carbonates, but consists almost 
entirely of an iron silicate, with very small percentages of clayey, 
calcareous, and phosphatic matter. 
Origin of marls. — The exact cause of the deposition of marls has 
been the subject of much investigation and discussion, particularly in 
the last few years, since they have become of economic importance. 
The most important papers concerning this question are as follows: 
Blatchley, W. S., and Ashley, G. H., The lakes of northern Indiana and their 
associated marl deposits: Twenty-fifth Ann. Rept. Indiana Dept. Geol. Nat. Res., pp. 
31-321. 
Davis, C. A., A contribution to the natural history of marl: Jour. Geol., vol. 8, 
pp. 485-497. 
Davis, C. A., Second contribution to the natural history of marl: Jour. Geol., vol. 9, 
pp. 491-506. 
Davis, C. A., A contribution to the natural history of marl: Rept. Michigan Geol. 
Survey, vol. 8, pt. 3, pp. 65-102. 
Lane, A. C, Notes on the origin of Michigan bog limes: Rept. Michigan Geol. 
Survey, vol. 8, pt. 3, pp. 199-223. 
Disregarding the points in controversy, which are of no practical 
importance, it may be said that marls are deposited in lakes by spring 
or stream waters carrying lime carbonate in solution. The actual 
deposition is due in part 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 distribu- 
al tion of marl deposits is intimately related to the geologic history of 
10 [the region in which they occur. Marl beds are the result of the filling 
of lake basins. Lakes are not common in the United States, except in 
areas which have been glaciated, since they are in general due to the 
11 damming of streams by glacial material. Workable marl deposits, 
' 1( therefore, are confined almost exclusively to those portions of the 
fl 
