158 The Ottawa Naturalist. 



doubtedly was a period in its history when rock structure, as we now 

 know it, did not exist. This theory, which is commonly styled " the 

 nebular hypothesis," most completely satisfies all the conditions required 

 and may be briefly stated thus. It supposes that in the beginning the 

 universe existed simply in a state of cosmic ether ; that this in process 

 of time gave off immense masses to which a rotary motion was imparted 

 through various forces; that from these whirling masses large rings were 

 separated, which by rupture and gradual condensation gradually assumed 

 a spherical shape, as a consequence of the rotary movement, till at 

 length the solar syste-n, with its central sun and accompanying planetary 

 bodies was evolved. 



The cosmic matter, in process of time cooled down sufficiently to 

 produce a crust, composed of various mineral constituents ; and the 

 cooling and hardening of the earth's mass pioceeded either from the 

 centre as a nucleus outward or by a gradual thickening of a first formed 

 crust inward. Several theories have been proposed to explain this 

 stage of the earth's history, but the greater number of physicists and 

 geologists at the present day regard the globe as a more or less solid mass 

 with areas of liquid matter at various points throughout the interior. Be 

 that as it may we can safely say that the first rock material was produced 

 by the gradual decrease in temperature of the original nebular mass, 

 and in this way a foundation was laid down for the subsequent 

 depositionof rock material, for the introduction of living organisms, and 

 finally for the advent of man himself. 



From a careful examination of many portions of this crust which 

 have been brought to the surface either by denudation of overlying 

 formations or by the extrusion of liquid matter, as in the case of 

 volcanoes, it has been ascertained to be composed of a number of 

 simple or undecomposable substances or elements of which about 

 seventy have now been recognized. Of these the greater part 

 apparently exist in very limited quantity, while the main mass of the 

 crust is made up of a few easily recognized compounds formed from 

 the union of two or more simple elements. The most abundant of 

 these is silica which is the result of a chemical union of silicon and 

 oxygen, and this constitutes more than half the mass of the earth's 



