Reviews. 



Department of Geology and Natural Resources of Indiana, Twenty - 

 fifth Annual Report. By W. S. Blatchley, State Geologist, 

 Indianapolis, Ind., 1900. Pp. 782. Maps and plates. 



The current report deals mainly with the cement resources of the 

 state. It opens with a short paper by the state geologist on Portland 

 cement, a compilation treating of its history, uses, composition, pro- 

 cess of manufacture, methods of testing, etc., together with a short his- 

 tory of the development of the industry in Indiana. 



The report on the Lakes and Marl Deposits of Northern Indiana 

 is the result of the joint work of the state geologist and and Dr. George 

 H. Ashley. It is a thorough report of some three hundred pages and 

 is accompanied by seventy maps of individual lakes on which the marl 

 deposits in their varying conditions of occurrence are represented by 

 conventional signs. In the body of the text, full physiographic 

 descriptions of the lakes are given, as well as the detailed economic 

 geology of the marl deposits. The notes on the natural history of 

 these lakes, which are appended to the descriptions, are of much inter- 

 est to the student of botanical ecology. 



It is found that a deposit of marl of a thickness of ten feet and cov- 

 ering 160 acres will supply a factory of 500 barrels daily capacity for 

 30 years. Such a supply is termed a " workable deposit " in the report. 

 There are thirty-two lakes which have at least that much marl available. 

 With improved methods of raising marl from deeper waters, the pro- 

 ductive area of these lakes will be much enlarged, and there will be 

 added to the number half as many more, whose deposits are for the 

 most part under water of greater depth than ten feet, the present limit 

 of accessibility. 



In regard to the origin of the marl the authors do not attribute 

 more than 1 per cent, to shells as a source. The immediate source 

 they believe to lie in the calcareous matter of the glacial clays which 

 reaches the lakes in the form of the soluble double carbonate, 

 CaH 2 (C0 3 ) 2 . This is believed, to be carried by subterranean rather 

 than superficial streams, because the marl deposits are found in 



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