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most geologists. He thinks that the strongest evidence for the existence of life in pre-Cambrian time is the high organization of the Cambrian fauna. While geologists will be ready to assent to the strength of this last argument, they will hardly be ready to regard it as the only strong reason for belief in pre-Cambrian life. To the very considerable number of fossil forms already found in pre-Cambrian rocks no reference is made.

The important question of the origin of the Archean is rather briefly dismissed. The discussion touching this question is much less full and much less satisfactory than that of Prof. Van Hise, recently published.^[1] Indeed, had Prof. Van Hise's discussion been published before Dr. Kayser's treatise, the latter author might have found a way out of some of the difficulties which seem to lie in his mind concerning the origin of the Archean.

An excellent feature of the book is the prefacing of the discussion of each system by a short account of the origin and history of its differentiation from underlying and overlying systems. Each system is discussed under the general heads of—1) Distribution and development; 2) Paleontology. Under the first head, it could have been wished that the structural relations of the systems had been more uniformly and sharply brought out. Such clear statements as that concerning the North American Devonian system, that it rests "conformably and without break on the Silurian, and is covered conformably by the Carboniferous" (page 111), are not always to be found. Where knowledge does not permit such positive statements, definite statements representing the degree of present knowledge would have been welcome. So, too, the relations of faunal and stratigraphical breaks are not always so clearly set forth as could have been desired in a text-book.

In the discussion of the Permian system, Dr. Kayser brings out the fact of wide-spread conglomerate formations (India, Victoria, Brazil, South Africa) in tropical latitudes and the southern hemisphere, which sometimes contain polished and striated stones very like those of glacial formations of later date. In Africa the Dwyka conglomerate rests on rock, the upper surface of which is smoothed and striated like rock beneath the modern glacial drift. Dr. Kayser indicates that the belief that these Permian conglomerate beds are of glacial origin has gradually gained ground. The flora succeeding the conglomer-