﻿ANHTVEBSAKY ADDEESS OP THE PKESLDENT. • xliii 



formation of crystals of felspar, which have been frequently found in 

 the copper- works of Mansfeld — the more remarkable as all attempts 

 to obtain them by direct fusion have hitherto failed. The first direct 

 synthetic experiments to obtain minerals artificially by igneous 

 fusion were made successfully by Berthier, followed in 1823 by 

 Mitscherlich. They obtained many crystallized simple minerals 

 identical with those of nature. These researches for a long time led 

 to the belief that fluidity by heat could alone have yielded such 

 results ; but within the last few years, and especially within a short 

 time, other researches have produced a conviction that water, com- 

 bined with heat and pressure, must have acted a very important 

 part in most of the operations ascribed to the action of heat and 

 pressure only, from the earliest periods of geological time. 



That an enormous pressure must take effect, even at moderate 

 depths, is self-evident ; and that a very high temperature prevails in 

 the interior of the earth is proved by the existence of volcanos in all 

 parts of the earth, which from time to time pour forth streams of 

 molten incandescent rock ; and that a heat sufficient to keep rocks 

 in a fused or viscid state has existed from the earliest geological time 

 is made manifest by the veins and intruding masses of granite and 

 the other eruptive rocks that penetrate all formations, from the 

 oldest to the newest strata ; for the cone of trap that traverses the 

 Carboniferous rock and rises to the summit of Arthur's Seat, Edin- 

 burgh, is now believed to be of tertiary age. That this internal 

 heat is permanent is further demonstrated by the increase of tem- 

 perature as we descend from a short distance below the surface, in 

 all parts of the earth where the experiment has been made. We 

 have thus undoubted proof of the existence of two of the three great 

 active agents in the laboratory of nature, heat and pressure. 



"Without assuming the existence of great internal supplies of 

 water or its elements, there can b'e no doubt that it must exist in 

 the interior of the earth to a vast extent. The amount of that 

 which is carried off by rivers must bear a small proportion to that 

 which, falling from the atmosphere upon the wide-extended surface 

 of the land, must be carried to great depths through porous rocks, 

 and by the innumerable cracks and fissures by which every rock is 

 more or less traversed. The existence of subterranean rivers and 

 .of accumulations of water at great depths is proved by artesian 

 wells ; and, as we know no limits to the downward extent of faults 

 and fissures, there is every probability that much of the water that 

 falls on the surface must penetrate to depths where a high tem- 

 perature exists ; as is shown by hot springs, the temperature of which 

 we know to have continued undiminished for centuries, and by the 

 enormous volumes of watery vapour poured forth by volcanos. It 

 probably reaches depths where the heat will bring it not only to the 

 boiling-point, but, under great pressure, to a far higher temperature. 

 According to the researches of Mr. Eobert Hunt, the rate of increase 

 of temperature, from about 100 feet below the surface, is 1° of Fahr. 

 for every 50 feet in penetrating through the first 100 fathoms ; 1° 

 for every 70 feet in the next 100 fathoms ; but when the depth ex- 



