458 ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 



The meridian lines are therefore more considerably curved in 

 the neighbourhood of the equator than at the poles, and the- 

 equatorial diameter of the earth is consequently greater by about 

 24 geographical miles than the polar diameter. This is of course, a 

 consequence of the revolution of the earth on its axis, and of the- 

 influence of centrifugal force. This influence could not, however, 

 have made itself felt, had not the earth been originally in a fluid, 

 or at least plastic condition, so that the depression at the poles 

 constitutes one of the most unequivocal proofs of the original 

 fluid condition of the globe. 



Assuming this fluid condition to have been owing to the pre- 

 valence of an extremely high temperature, we are necessitated to> 

 suppose that the atmosphere was then very differently constituted 

 than it is at present. This has been remarked by many previous 

 writers. Dr. Hunt describes it as ' an atmosphere holding in the 

 state of acid gases all the carbon, the sulphur and the 

 chlorine, besides the elements of air and water."* Quensted re- 

 marks : " According to the igneous theory the whole of the sili- 

 ceous rocks were originally in lava-like fusion. It follows of 

 course that not only the whole of the sea must have existed in the 

 atmosphere, but also a multitude of substances, which could not 

 exist otherwise than in the gaseous state, such as carbonic acid, 

 chlorine, sulphur, elc."f These inferences are legitimately drawn,. 

 The sandstones, shales, and the fixed parts of the limestones of sedi 

 mentary formations then existed in the fused matter, along with, 

 the materials of the igneous and primary rocks, the soda of sea- 

 salt and the inorganic constituents of plants and animals. On the- 

 other hand, the carbonic acid of the limestones must have existed 

 in the atmosphere. The chlorine of the sea salt also could scarcely 

 have existed anywhere else than in the atmosphere in combination 

 with hydrogen, or with those metals which form with it volatile 

 chlorides, such as lead, zinc, copper, iron, cobalt, nickel,, 

 etc. Those volatile chlorides, which are decomposable while 

 in the gaseous state by oxygen, (such as those of the three 

 metals last named) could not however have existed in an atmos- 

 phere containing free oxygen, but it would seem, that the 

 primitive atmosphere did not contain any such free oxygen. 

 Bischof first adopted this view. He maintains that the carbon 

 disseminated through the dark clay slates of the pre-carboniferous 



* Canadian Naturalist, p. 202. 

 f Epochen der Natur. p. 20. 



