34: ANNUAL OF SCIENTIFIC DISCOVERY. 



continued there till the end of time, notwithstanding any igneous operations 

 which the materials might have afterwards undergone. But as the discovery 

 of very minute traces of phosphoric acid, when mixed with the other ingre- 

 dients of a rock, is a problem of no small difficulty, an indirect method of 

 ascertaining its presence suggested itself to me in some experiments of the 

 kind which I have instituted, namely, that of sowing some kind of seed, such 

 for instance as barley, in a sample of the pulverised rock, and determining 

 whether the crop obtained yielded more phosphoric acid than was present in 

 the grain, it being evident that any excess must have been derived from the 

 rock from which it drew its nourishment. Should it appear by an extensive 

 induction of particulars that none of the rocks lying at the base of the 

 Silurian formation, which have come before us, contain more phosphoric acid 

 than the minute quantity I detected in the slates of Bangor, which were 

 tested in the above manner, it might perhaps be warrantable hereafter to 

 infer that we had really touched upon those formations that had been 

 deposited at a time when organic beings -were only just beginning to start 

 into existence, and to which, therefore, the term azoic, assigned to these rocks 

 by some of the most eminent of our geologists, might not be inappropriate. 

 The proofs of the former extension of glaciers in the northern hemisphere, 

 far beyond their actual limits, tend also to complicate the question which has at 

 all times so much engaged the attention of cosrnogonists with respect to the 

 ancient temperature of the earth's surface ; compelling us to admit that at 

 least during the latter of its epochs, oscillations of heat and cold must have 

 occurred to interfere with the progress of refrigeration which was taking 

 place in the crust. On the other hand, facts of an opposite tendency, such ay 

 the discovery announced by Captain Belcher of the skeleton of an ichthyo- 

 saurus in latitude 77, and of the trunk of a tree standing in an erect position 

 in latitude 75, have been multiplying upon us within the same period : inas- 

 much as they appear to imply that a much higher temperature in forrnei 

 times pervaded the Arctic regions than can be referred to local causes, and 

 therefore force upon us the admission, that the internal heat of the nucleus 

 of our globe must at one time have influenced in a more marked manner than 

 at present the temperature of its crust. On the causes of this increased 

 temperature, whether local or cosmical, much elaborate research has been 

 brought to bear by Sir Charles Lyell and by Mr. Hopkins. The most 

 extensive collection of facts, however, having reference to this subject, is con- 

 tained in the Reports on Earthquake Phenomena, published by Mr. Mallet, 

 supplying, as they do, data of the highest importance to the full elucidation 

 of the subject. For although the evidence I have myself brought together 

 in my work on Volcanoes might be sufficient to establish in a general way the 

 connexion of earthquakes with that deep-seated cause which gives rise to 

 the eruptions of a volcano, yet our interest is thereby only the more awakened 

 in the phenomena they present, just as Dr. "Whewell's inquiries into the 

 local variations of the Tides were valued all the more hi consequence of the 

 persuasion already felt, that lunar attraction was their principal cause. But 

 if earthquakes bring under our notice chiefly the dynamical effects of this 

 r .idden cause of movement and of change, those of volcanoes serve to reveal 



