Geology. 319 



versity in the spring of 1914. The work contains eight chapters, 

 corresponding to the number of lectures given. It should be 

 stated at the outset that the author uses the term " volcanism " in 

 its broadest sense to include the varied forms in which the igne- 

 ous activity of the earth manifests itself. His purpose has been 

 to present the problem of volcanism in this sense, rather than a 

 theory or a supposed explanation of it. And since any concep- 

 tion of the problem must be modified, not only by our knowledge 

 of the physical properties of the earth as a whole, but by its 

 origin and astronomical relations, these phases of the subject are 

 also treated. 



The first chapter undertakes a brief review of the material for 

 discussion : various types of volcanic activity, both extrusive and 

 intrusive, are described with mention of their geographical dis- 

 tribution ; and in this way the problem which is to be treated is 

 laid briefly before the reader. 



In the second chapter the author takes up the nebular hypothe- 

 sis for the origin of the earth, and reviews it historically, com- 

 mencing with Buffon and Kant. He shows that the conceptions 

 of Laplace, in the general form postulated b}^ him, are still appli- 

 cable, though the particular hypothesis in which it has been 

 restated by geologists under his name may be no longer tenable. 

 He shows how the idea of the nebular origin of the planetary 

 system has grown and how greater knowledge of nebula? has 

 affected it ; carrying the discussion down to the conceptions of 

 Chamberlin and Moulton, who have treated it from mathematical 

 and physical standpoints. The author concludes w T ith the state- 

 ment that "It seems reasonable to assume that nebulae are not 

 highly heated ; that exploding and expanding matter, if finely 

 divided and distributed through an enormous space, would cool 

 far below its former temperature, if derived from a disrupted sun ; 

 that subsequent aggregation would be a very gradual process, and 

 that whatever heat were generated by impact w r ould be dissipated 

 without considerable rise in temperature ; that the heat of con- 

 densation might be a principal source of internal heat in a globe 

 so formed, but that its amount would be greatly modified by the 

 size and mass of the aggregation, the physical character of its 

 components, and by the time occupied in its growth." 



In the next chapter the general physical characters of the earth 

 as a whole are considered ; its relief, variations of gravity, nature 

 of its outer shell, etc., and the conclusion is reached that the earth 

 is a heterogeneous elastic solid, subject to accumulating stresses 

 that periodically exceed the limit of elasticity and cohesion. This 

 chapter is followed by one dealing in a general way with the more 

 important penological features of the rocks composing the earth's 

 outer shell ; and is succeeded by the fifth one, treating of the 

 dynamical status of the earth, in which conceptions as to its possi- 

 ble interior constitution and physical and chemical properties are 

 advanced, postulated on an origin from a nebular condition in 

 agreement with the author's viewpoint. 



