312 ANNUAL OP SCIENTIFIC DISCOVERY. 



only upon limited masses and in limited areas; it might also act in a more 

 general manner, and from as general a source as the whole interior mass of 

 the earth. It was necessary to refer distinctly to the possibility of the last 

 source of metamorphic calorific agency, as it was sometimes called in ques- 

 tion by gentlemen of very high authority. There are, however, abundant 

 reasons for believing that, at a comparatively mall depth beneath the earth's 

 surface, heat exists sufficient to melt the most refractory rocks. A conclu- 

 sion announced by Mr. Hopkins is supposed by some geologists to render 

 these results inadmissible. But this conclusion requires for its establishment 

 conditions in the structure of the earth which Mr. Hopkins does not prove, 

 but which he is compelled to assume, in order to reduce his equations to 

 numbers. Instead of assuming conditions, Mr. Hennessey was led to inquire 

 what would be the most probable structure of the earth, if the formation of 

 its solid crust followed the physical laws which are observed on the solidifica- 

 tion of fused masses of rock. It follows from the whole of his inquiries, 

 that not only do we possess no reasons for believing that the earth's crust 

 has a thickness so great as that announced by Mr. Hopkins ; but that its lim- 

 iting thickness will probably be found to depend upon the limit of fusibility 

 of the substances of which it is composed. There could, therefoi-e, be no 

 difficulty in perceiving how, during remote geological epochs, the earth's 

 crust might be so thin as to allow a very important influence to be exercised 

 by the high temperature of the interior fluid matter on the structure of the 

 Sedimentary strata deposited on the outer surface of the solidified crust. 



EXPERIMENT ON THE MELTING AND COOLING OF BASALT. 



At a recent meeting of the Manchester Society of Engineers, Mr. Hawkes 

 described an experiment recently made by him on the melting and cooling 

 of basalt. About 31 cwt. of basalt was melted in a large double reverbera- 

 tory furnace, and after a slow cooling during thirteen days, it presented an 

 upper stratum of stony vesicular matter, about one inch thick, next a layer 

 of black glass, from two to eight inches deep on that side of the mass which 

 was exposed to the air from the door of the furnace (elsewhere, immediately 

 under the vesicular layer Avas solid stone, interspersed here and there with 

 air-bubbles). Mr. Hawkes added some observations relating to the results of 

 experiments which he had made to ascertain the temperature of melted cast- 

 iron, and of melted basalt. 



AECTIC GEOLOGY. 



One of the most important results brought out by recent Arctic Explora- 

 tions, is the seeming establishment of the conclusion, long since announced, 

 that the sea temperature of the arctic zone in the Silurian, Devonian, and 

 Carboniferous ages, was not essentially different from that in the temperate 

 zone. The study of the geographical distribution of animals is showing that 

 species have but a narrow range of temperature in which they can flourish 

 in full vigor, and even families and tribes have often but a limited range. 

 20 F. (between 68 and 88) is the whole range of the existing coral reef 

 corals and species have still more restricted limits. The existence, there- 

 fore, of the same species of corals, molluscs and trilobites, or of closely re- 

 lated or representative, if not identical, species, in latitudes 40 and 75, leads 

 to but one conclusion. The near uniformity of the climate is at once sug- 

 gested, and mutft be admitted until this life-thermometer reads otherwise. 



