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THE GEOLOGIST. 



The interior higher temperature of the earth, the higher climatal 

 temperature of the early geological periods, the lower tempera- 

 ture of the glacial periods, the earth's form and density, together 

 with the astronomical phenomena of the precession of the equinoxes, 

 and the corresponding inequality in the moon's motion, must all be 

 accounted for by any complete geological theory. In proceeding, then, 

 to theoretical considerations, in the first place we may remark that the 

 spheroidal form of the earth could not fail to suggest the idea of fluidity 

 — a state to which no conceivable cause but excessive heat could reduce 

 it, but which was not necessarily the earth's primitive state, but an 

 antecedent state through which it must have passed before it became 

 solid. 



Moreover, the observed increase of temperature in descending beneath 

 the earth's surface suggested the notion of a central incandescent nucleus 

 still remaining in a state of fluidity from its elevated temperature. 

 Hence the theory that the exterior crust had assumed its present solidity 

 by the radiation of heat into surrounding space and its consequent 

 refrigeration. 



This central heat was formerly thought a sufficient cause for the more 

 equable climate over the earth's surface at remote geological periods ; but 

 it manifestly could not account for a temperature in this glacial period 

 so much colder than at present. This fact has led to a more careful 

 investigation of these causes, and these are found in the relative dispo- 

 sition of land and sea, and the effects to be more especially influenced by 

 the ocean-currents of warmer or colder water. 



The influence of the Gulf-stream upon our own climate is well 

 known, and with such a powerful example of climatal alteration before 

 us, we must be cautious how we appeal to other causes as necessary to 

 account for a higher temperature. 



The rival theory of this primitive and central heat is that which 

 attributes the internal terrestrial temperature, as well as volcanos, to 

 cJiemical action. 



The question of a continuous progression of our globe from a primi- 

 tive towards a final physical state considered with reference to the 

 evidence supplied by organic remains on the question of progres- 

 sion or non-progression, has, perhaps, been more or less associated in 

 the minds of speculative geologists with that of the trajismutation or 

 perniatienee of s^Mcies. 



Mr. Hopkins discusses here the necessary distinction of a species ; 

 but without following him in those remarks, we enter at once into the 

 main topic. 



The question really involved is that of the transmutation or perma- 

 nence of species is, whether species— using the term in its wider and 

 more unrestricted sense — have any existence in nature or not. 



That different races of animals have been introduced on the face of 

 the globe at successive epochs, is testified by their fossil remains, hence 

 the question of transmutation or permanence of species has a high 

 geological interest ; and those who wish to study the details of this ques- 

 tion, may refer to Sir Charles Ly ell's presidential address to the 



