226 ANNUAL OF SCIENTIFIC DISCOVERY. 



deposits of fossil fuel have been derived from the decomposition of 

 this excess of carbonic acid by the ancient vegetation. In this 

 connection the vegetation of former periods presents the phenom- 

 enon of tropical plants growing within the polar circle. Prof. T. 

 Sterry Hunt considers as unsatisfactory the ingenious hypotheses 

 proposed to account for the warmer climate of ancient times, and 

 thinks that the true solution of the problem is to be found in the 

 constitution of the early atmosphere, when considered in the light 

 of Dr. TyndalTs researches on radiant heat. He has found that 

 the presence of a few hundredths of carbonic acid gas in the at- 

 mosphere, while offering almost no obstacle to the passage of the 

 solar rays, would suffice to prevent almost entirely the loss by 

 radiation of obscure heat, so that the surface of the land beneath 

 such an atmosphere .would become like a vast orchard-house, in 

 which (he conditions of climate necessary to a luxuriant vegeta- 

 tion would be extended even to the polar regions. Mech. Mag. t 

 August, 1867. 



NATURE OF GRANITE. 



The effect of the internal heat of the earth upon the buried 

 sediments in early geological times would be to soften them, 

 produce new chemical reactions between their elements, and 

 convert them into what are called crystalline or metamorphic 

 rocks, such as gneiss, greenstone, granite, etc. It is often said 

 that granite is the primitive rock or substratum of the earth, but 

 this is not only unproved, but, in the opinion of Prof. T. S. Hunt, 

 extremely improbable. He considers that the composition of this 

 primitive rock, now everywhere hidden, must have been much 

 like that of a slag or of lava, and that there are good chemical rea- 

 sons for the belief that granite is in every case a rock of sedimen- 

 tary origin, made up of materials deposited from water, in- 

 cluding in its composition quartz, which, so far as known, can 

 only be generated by aqueous agencies, and at comparatively low 

 temperatures. 



Prof. Ansted read a paper before the British Association, in 

 1867, on the conversion of stratified rock into granite. Geologists 

 until recently have spoken of granite as a primitive rock, as the 

 nucleus of the earth, and as having been from time to time 

 erupted, playing an important part in the general disturbances by 

 which the framework of the earth is supposed to have been con- 

 structed. The observations of Daubree and Sorby show that all 

 true granite had been elaborated with water under great pres- 

 sure, at a temperature below melting heat; that it had neither 

 been ejected, nor had it formed a framework. There are granites 

 of all ages, and of many kinds. Numerous observations show 

 that granite alternates with and passes into stratified rocks, and 

 must itself in such cases be stratified rock, and that its production 

 does not necessarily involve the destruction and obliteration of all 

 the stratified rocks with which it is associated. This view of the 

 nature of granite will greatly affect the theories of geology. 



