Reviews 



Origin of the Bighorn Dolomite of Wyoming. By Eliot Black- 

 welder. Bull. Geol. Soc. Am., XXIV, 607-24, plates 8, 

 December 22, 1913. 

 The Bighorn dolomite is widely distributed in northwestern Wyo- 

 ming. Its fossils, mostly corals and crinoid stems, are rare and seldom 

 well preserved, but indicate an Ordovician age, possibly including 

 Silurian also. Chemically the formation is a very pure, normal dolomite, 

 with very little terrigenous matter. Its weathered surface is character- 

 istically coarsely pitted and fretted, owing, not to intermingling of sili- 

 ceous with calcareous matter, but to compact fine-grained dolomite 

 structures imbedded in a matrix of more coarsely crystalline and porous 

 dolomite. The ill-defined branching patterns due to differential weather- 

 ing are probably of organic origin, more likely representing banks of 

 calcareous algae than plantlike animals. The obliteration of original 

 organic structures is assigned to the process of crystallization of the 

 dolomite, probably taking place almost simultaneously with deposi- 

 tion on the sea floor. The deposits were doubtless made in an epicon- 

 tinental sea less than 100-120 meters deep. 



R. C. M. 



On Oceanic Deep-Sea Deposits of Central Borneo. By G. A. F. 

 Molengraaff. Koninklijke Akademie van Wetenschappen 

 te Amsterdam, Proceedings of the meeting Saturday, June 26. 

 1909. Pp. 7, map 1. 

 The Danau formation, which outcrops over an area of approxi- 

 mately 40,000 sq. km. in central Borneo, consists of cherts and hornstones 

 formed almost entirely from the tests of Radiolaria. The char- 

 acter of the formation is very constant throughout the area. It consists 

 of two types: the one, a true Radiolite, is semitransparent, hard, and 

 brittle, with a color varying from milk-white to red or green, and is 

 composed almost exclusively of the closely packed tests of Radiolaria; 

 the other is an argillaceous chert, always, red in color. The latter con- 

 tains fewer Radiolaria and is analogous to modern deep-sea red clay 

 deposits. The former corresponds to Radiolarian ooze. This large 



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