REVIEWS 87 



Following these valuable contributions to the general subject of cements comes 

 the directory proper. This contains lists of American cement manufacturers ; cement 

 brands; sales agents ; foreign cement manufacturers ; dealers in cement ; contractors, 

 engineers, and other large users of cement ; cement-testing laboratories ; manufac- 

 turers of cement machinery; manufacturers of hme ; plaster plants; and dealers in 

 lime and plaster. 



Clarke, F. W. Analyses of Rocks, Laboratory of tJie U. S. Geological Sur- 

 vey, 1880 to i8gg. Bull. 168, U. S. G. S. 8vo, pp. 308, 1900. 



Contains many analyses of building stone and other material of economic 

 interest. 



Coons, A. T. The Stone Industry in igoi. Extract from Mineral Resources 

 U. S. for 1901. 8vo, pp. 67, IQ02. 



The value of the stone produced in the United States during 1901 is given as 

 $56,615,926. This total includes granite, $14,266,104; trap, $1,710,857; marble, 

 $4,965,699; limestone, $21,747,061; slate, $4,787,525; sandstone, $6,974,199; and 

 bluestone, $1,164,481. 



CUMMINGS, Uriah. \Prodiiction of] American Rock Cetnent [in the U. S. 

 during I go6\. Mineral Resources U. S. for 1 goo. Pp. 745, 746, igoi. 



Resume of the condition of the American natural cement industry during 1900, 

 with statistics of production. 



Davis. C. A. A Contribution to the Natural History of Marl. Journ. Geo!., 

 Vol. VIII, pp. 485-97, 1900. 



The influence of lower forms of plant life upon the formation of siliceous sinter, 

 calcareous tuffs, etc., in the neighborhood of hot and mineral springs has been dis- 

 cussed by Weed and Cohn. In the present paper the relation of certain low plant 

 forms to the formation of marl is treated in detail, special attention being given to 

 marl deposits of the type commonly found in Michigan. 



The Michigan marl (excluding its contained vegetable matter) is, undoubtedly, 

 derived ultimately from glacial clays and disintegrated rock masses. These clays are 

 rich in finely divided limestones, and in rock-forming minerals containing calcium 

 compounds. Percolating waters, carrying carbon dioxide in solution, readily take up 

 the calcium salts, to a certain limit. If the amount of carbon dioxide contained in the 

 water be considerable, part of it will escape whenever the pressure is lowered. This 

 should result in the precipitation of a corresponding part of the calcium carbonate. 

 As the streams of the area under consideration do not deposit marl where they reach 

 the surface, and as the waters of those springs and streams show no milkiness on 

 exposure to ordinary atmospheric pressures and temperatures, it is inferred that no 

 large amount of carbon dioxide is carried, and that there is no approach to the satura- 

 tion point for calcium bicarbonate in the springs and streams of the Michigan marl 

 region. 



Three alternatives are therefore left: (i) the marl was formed under conditions 

 differing from those at present ; (2) the amount of dissolved salts is so small that the 

 saturation point is not approached until after the lakes are reached and the slow 

 evaporation and reduction in the amount of dissolved carbon dioxide brings about 



