606 Scientific Intelligence. 



later years have brought forth. Professor Rice, as a student of 

 Dana's and one who grew up in that period of profoundly 

 changing thought, the third quarter of the nineteenth century, is 

 qualified from personal experience to give this historic introduc- 

 tion and show the relations of present geologic research to that 

 of the previous generation. 



Chapter II deals with the Problems of the Canadian Shield — 

 the Archeozoic. The author is Frank Dawson Adams. Within 

 the Canadian Shield are displayed the oldest known rocks of the 

 continent ; rocks which have been reinterpreted within the 

 present generation and give knowledge of what may be called the 

 heroic period in the history of the earth. The author begins by 

 considering the present limits and physiography of this shield 

 and the older of the rocks which constitute it. The granite 

 gneisses are found to be intrusives of widely different ages. The 

 studies of the nature of these igneous rocks and of their mode ot 

 intrusion are of the highest interest. 



Dr. A. P. Coleman, in Chapter III, takes up the study of the 

 Proterozoic of the Canadian Shield. The striking features of 

 the deposition and metamorphism of the Sudbury Series are de- 

 scribed and an interpretation is given of the physiographic and 

 climatic conditions of Sudburian time. The Sudburian was fol- 

 lowed by a great interval of igneous intrusion, of mountain uplift 

 and erosion which separated it from the true Huronian. In the 

 renewal of the sedimentary record which took place then, the 

 Huronian tillites, as evidence of glacial climates, easily hold first 

 place in present interest. The closing parts of the chapter deal 

 with the deposits of the Animikie and Keweenawan periods. 



The opening of the Paleozoic is dealt with by C. D. Walcott 

 in Chapter IV, under the title of " The Cambrian and its Prob- 

 lems in the Cordilleran Region." The progress of the Cambrian 

 seas across the peneplained surface of older rocks is described and 

 numerous sections of the sediments are given. In the interpre- 

 tative portion : in lower Cambrian time the evidence is regarded 

 as indicating a warm climate becoming colder toward its close. 

 In Middle Cambrian time the climate was temperate and equable. 

 In the Upper Cambrian it became more varied. Finally there is 

 given a review of the remarkable life record which Walcott has 

 recovered from these Cambrian formations. 



Chapter V, The Igneous Geology of the Cordilleras and its 

 Problems is by Waldemar Lindgren. He concludes that the 

 character of the igneous rocks from the earliest to the latest times, 

 changing in successive eras, calls for at least three magma basins of 

 primary importance ; the first, acidic ; the second, basic ; the third, 

 intermediate in composition. The original relations of these in 

 the earth, their causes and modes of irruption and eruption form 

 the problems which are discussed in the latter part of the chapter. 



Chapter VI is by F. L. Ransome, of the United States Geolog- 

 ical Survey, on the Tertiary Orogeny of the North American 

 Cordillera and its Problems. Descriptions of the orogenic lines 



