472 Reviews — T. C. C/iamherlin 8f E. D. SaUshiiry — 



The bottom of the lake, composed of soft Jurassic clay, was 

 gradually deepened, pari passu with the excavation of the gorge, the 

 deepest part being always, as shown on the contour maps, near the 

 mouth of the latter, where the erosive power of the escaping water 

 was the greatest. 



la IB ^v I E -v^ s. 



I. — Geology : Earth History. By T. C. Chamberlin and 

 E. D, Salisbury. Vol. II : Genesis-Paleozoic ; pp. xxvi, 692, 

 with 306 illustrations. Vol. Ill: Mesozoic-Cenozoic ; pp. xi, 

 624, with 576 illustrations. (London : John Murray, 1906. 

 Price 21s. each net.} 



N continuation of the account of " Processes and their Results," 

 reviewed in our August number, we now call attention to the 

 second and third volumes. They complete this great geological 

 work, and aim at giving an interpretation of the record of the rocks, 

 based on acquired knowledge. In the second volume the story 

 opens with matter that is necessarily more or less imaginative or 

 speculative, matter requiring astronomical, physical, and chemical 

 knowledge, not of great practical moment to the geologist, but 

 full of interest to those who wish to start " In the beginning," 

 with Nebular and Meteoritic hypotheses of the earth's origin ; 

 with Cosmology in fact, about one-fifth part of the volume is 

 occupied ; and many points briefly mentioned in the first volume 

 are here amplified. 



The authors adopt a modified Nebular, or Planetesiraal, hypothesis, 

 and mark out the stages of the earth's evolution as (1) astral, 

 (2) molten, and (3) lithic eons, with a practically solid globe; 

 leading on to (4) a primitive volcanic eon, accompanied at first by 

 prodigious volcanic activity, and later attended by sedimentation and 

 the introduction of life. In this last eon we pass from the unknown 

 into the partially known ; into the oldest accessible formations, 

 classed in the Archeozoic era. This is the era of schists and 

 granitoid rocks, a complex series including outflows of lava, 

 A'olcanic tuff's, igneous intrusions of various types, together with 

 sedimentary rocks ; all more or less highly metamorphosed, 

 crumpled, and deformed. The presence of life is suggested by 

 carbonaceous shales, certain iron-ores, limestones and cherts, similar 

 to those which owe their origin in part to organic action. This 

 era, it is thought, may have exceeded that of all subsequent time. 



Between the Archeozoic and the next era represented in the 

 rocks, there is everywhere great unconformity. This next phase 

 is termed the Proterozoic (a synonym for Algonkian as used by the 

 U.S. Geological Survey). The term is apt to be confused with that 

 of Protozoic suggested by Murchison in 1839, and adopted by 

 Lapworth for the Lower Palaeozoic (Cambrian, Ordoviciau, and 

 Silurian). 



In this Proterozoic era it may be said that geological history 



