A. C. Lane — Divisions of the Pre- Cambrian. 483 



with wlioni Credner was associated. This rather rare paper was 

 probably not at his hand. Credner was one of the earliest writers to 

 advocate substantially the dual division of Van Hise, though with 

 other nomenclature, thus : — 



-n, . ( Huronian. 



JliOZOlC { T i.- 



( Laurentian. 

 It strikes the author as a pretty good nomenclature, well worthy 

 a few moments discussion by Van Hise. 



It seems to him, however, and he does not wish this paper to bd 

 purely critical, that there will be such a dual division, on a sound 

 philosophic and ' zoic ' basis, though not exactly on the line laid 

 down by Van Hise. 



There has been much discussion of late of desert sedimentation, by 

 Walther, "W. M. Davis, Barrell, Huntington, and others. It seems to 

 the writer that many of the peculiarities of the desert are due, not to 

 the arid climate ji^^r se, but to the fact that it is devoid of vegetation. 

 This we now find practically only in arid lands, but before the earth 

 was clothed with verdure, or moss or lichen existed, the land must 

 have been bare, and even though the climate were wet the sedi- 

 mentation must have been very different. In particular, without the 

 organic acids there must have been little chemical denudation by 

 organic acids and carbon dioxide. This had an effect in two ways. 

 In the first place, the streams contained little carbonates and yielded 

 little to the ocean. In the second place, the sediments formed by 

 disintegration of the rocks, which mechanically is much more 

 active when not protected by vegetation, must have been much richer 

 in the soluble bases, which would otherwise have been removed by the 

 organic acids. In this way were produced the ancestors of the arkoses, 

 greywackes, and sedimentary gneisses and schists. Thus the peculiar 

 character of the early sediments upon which Van Hise comments may 

 have a direct ' zoic ' meaning. jS^or is this the whole story. The 

 subtraction of organic additions and disintegration leaves the other 

 kind of chemical activity more important — the volcanic exhalations, in 

 which there is reason to believe chlorine and sulphur emanations were 

 prominent, would still exist, and in fact there was volcanic activity 

 and agglomerates on a large scale. These acid radicals would, 

 however, tend to carry off the iron to the sea and not precipitate it as 

 the carbonate radical does. We should, therefore, have had in the 

 Azoic ocean at the end an accumulation of chlorides of calcium, iron, and 

 other bases, and its sediments composed of volcanic agglomerates and 

 conglomerates, and mechanical sediments, like arkoses and gneisses 

 and mica - schists, differing but slightly from the associated igneous 

 rocks. Now this is the character of the oldest rocks, the Keewatin 

 series, and analyses indicate that the early ocean was relatively a 

 solution of calcium chloride, while Quinton's very plausible theory, 

 especially with the modifications suggested by the writer,' implies 

 a relatively fresh ocean. Such, then, would be the Azoic, the early 

 part of the pre -Cambrian. 



1 "The Early Surroundings of Life," Science, 1907, vol. xxvi, p. 129; "The 

 Chemical Evolution of the Ocean," Journal of Geology, 1906, vol. xiv, p. 205 ; 

 Bull. Geol. Soc. Amer., 1907, vol. xvii, p. 691. 



