240 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



the Algonkian series of formations,* but the origin of the great pre- 

 Cambrian limestones of western America has long been a mooted 

 question, and the nature of the concretionarylike Cryptozoon (pi. 2) 

 has not been so definitely determined as to be accepted by common 

 consent either as of plant or animal origin. Twenty years ago I had 

 a number of thin sections made of the matrix and " fossils " from 

 the limestone of the Chuar terrane of the Grand Canyon series of 

 Arizona^ and later of specimens from the Belt series of Montana. 

 Not being able to discover any traces of detailed or minute structure, 

 the specimens and slides were put aside for future study. Recently 

 I have had occasion to consider the question of the origin of the 

 limestones of the great pre-Cambrian Algonkian formations of the 

 Cordilleran area, and in this connection to determine if possible 

 whether there was any relation between the so-called Cryptozoon 

 and the presence of the Algonkian series of limestones. 



The carbonaceous matter in the dark Newland limestones is shown 

 by the black, flocculent residue that accumulates when a fragment of 

 limestone is dissolved in hydrochloric acid and by the bituminous 

 odor given off when the rock is struck with a heavy hammer. This 

 carbonaceous matter was probably derived from the bacteria and algse 

 of the time.^ 



The limestones of the Newland formation have more or less mag- 

 nesian content, but many of the layers are pure limestone, especially 

 those containing the reefs or banks of algal remains. The specimens 

 of algal remains are usually magnesian and siliceous, which accounts 

 for the weathering in relief (pis. 2 and 3) and the ease with which 

 they are etched by the solution of the limestone in weak hydro- 

 chloric acid. 



The purer limestones are of considerable vertical thickness and 

 their distribution indicates bodies of water several thousand square 

 miles in area. The banks or reefs of algal deposits make a small 

 percentage of the total mass of limestone, but if we assume, as I think 

 we may, that the bacteria were active agents in the deposition of 

 the soluble bicarbonate of lime in Algonkian waters, a plausible ex- 

 planation is found for the occurrence of the homogeneous limestones 

 of the Algonkian in which no traces of fossils have been found.* 



FOSSIL BACTERIA. 



The occurrence of bacteria in a fossil state has long been known. 



Dr. Clement Reid, in an article on Paleobotany, states that^ — 

 the first evidence for the existence of Paleozoic bacteria was obtained in 1879 

 by Van Tieghem, who found that in silicified vegetable remains from the coal 



1 Smithsonian Misc. Coll., vol. 64, no. 2, 1914, p. 89. 



2 Cryptozoon t occidentale Dawson, Bull. Geol, Soc. America, vol. 10, 1899, pp. 232-234, 

 pi. 23, figs. 1-4. 



3 Pre-Cambrian Algonkian algal flora, Smithsonian Misc. Coll., vol. 64, no. 2, 1914, p. 95. 

 * Idem, p. 94. 



» Encyclopaedia Britannica, 11th ed., vol. 20, 1911, p. 525. 



