The Origin of the Earth. 281 



a planet ; or it may be captured by the attracting star and become 

 its planet ; or finally it may be snot off into space and escape from 

 the influence of both bodies and give rise to a comet or swarm of 

 meteorites. The tide may cause projections at opposite sides of the 

 parent star, and the matter shot out may, it is held, remain connected 

 to the parent by a nebular band, and thus give rise to a spiral 

 nebula with the usual two arms. Professor Chamberlin suggests 

 that the detached nebulous mass of the nebula M51 in the con- 

 stellation of the Hunting Dogs was due to a mass which was torn 

 from the main nebula by the disruptive approach of another star and 

 was left connected to it by a nebulous band. 



According to Professor Chamberlin' s theory, as the spiral nebulae 

 are due to the dynamic disruption of a compact and possibly cold 

 star, they do not represent the original condition of matter. They 

 are apparently an ephemeral stage in the life-history of solar systems. 

 The genesis of such systems is therefore pre-nebular. If nebulae are 

 due either to direct collision or dynamic disruption their life should 

 be comparatively short. The stars which blaze up in consequence of 

 hypothetical collisions lose their sudden brilliancy in a few weeks or 

 months ; and if the light of the nebulae is due to incandescence it ought 

 soon to wane. The author has clearly shown the fundamental diffi- 

 culties in Laplace's theory ; but the nebulae remain one of the most 

 perplexing enigmas of the heavens. Indeed, several features in the 

 solar system, such as the uniform direction of rotation of the vast 

 majority of its members, in regard to the reasonable explanations 

 that have been offered for the insignificant exceptions, agree better 

 with the requirements of Laplace's theory than with that of the 

 formation of nebulae by Roche's dynamic disruption. 



The second part of the book deals with the less speculative problems 

 of geographical evolution, and it is interesting to note that the author, 

 approaching the subject by his special route, lays much stress on the 

 arrangement of the continents and the oceans as six interlocking 

 triangles arranged around the Equator, on the antipodal position of 

 land and water, and on the periodic variations of the major geographical 

 processes in consequence of the deformation of the earth's crust. 

 These views have been advocated in connexion with the tetrahedral 

 hypothesis, to which the author does not refer. The conclusion in 

 this part of the work to which many geologists are most likely to 

 dissent is the adoption of the permanence of oceans and continents in 

 an extreme form. The author attributes the position of the major 

 elevations and depressions on the earth's crust to influences which 

 acted upon it during its primary consolidation. Lord Kelvin adopted 

 that conclusion and attributed the continents to segregations in the 

 earth while it was still gaseous. Professor Chamberlin suggests they 

 may be due to certain parts of the earth's surface having been cooled 

 by descending currents of air in the anticyclones of the earth's 

 primitive atmosphere. 



The book deserves attention by all geologists interested in the 

 early history of the earth, and can be read with interest by any 

 student of either geology or geography. It gives comparatively few 

 references ; but those given are of special use to geologists by 



