134 R. Mallet— Reply to Mr. Poulett-Scrope. 



at whatever depth, holds as much v/ater as the most highly hydrous igneous 

 rocks known at our surface, — that is, at a maximum about two, and on the 

 average less than one per cent, by weight. Has Mr. Scrope ever calculated 

 what supply of steam for elevation and waste this would afford him from a 

 column of his hquefied hydrous rock of, say, a mile square, and sixty miles in depth? 

 The pressure at the base of such a column of the density of granite would be more 

 than 20,000 atmospheres. Has Mr. Scrope ever considered what amount of ex- 

 pansion his vesicular water could undergo under such a pressure and at a tempe- 

 rature equal to that of melted lava, or, if he likes, much higher? Has he considered 

 the bearing on this of Dr. Andrew's late researches upon the expansion of liquids 

 at great pressures and temperatures, and of the temperature at which it is probable 

 from these "the critical point" for water is reached, or the effect upon the tem- 

 perature of the column of the steam bubbles expanding in proportion 'to their 

 distance from the base ? Suppose these and other formidable physical difficulties 

 removed, and that such a column could be lifted by the machinery assigned, the 

 expansion of the evolved steam is at every point in the height of the column, 

 whose temperature we may even grant to be constant throughout, proportionate to 

 its depth in the column; it is, as we have supposed, 20,000 atmospheres at the base, 

 and one atmosphere at the top of the column. Once this equilibrium is obtained, 

 even slow frothing over or overflow of the column at the surface, much less 

 reiterated spirting and ejection, is impossible. Any analogy to the champagne 

 bottle is merely delusive. But again, how can we account on such a mechanism 

 for that pulsatory ejective action which characterizes all volcanic eruption ? — for 

 those roaring blasts of steam, recurrent at uncertain intervals, which Mr. Scrope 

 himself has so well referred to, in the preceding part of his remarks, as resembling 

 the volley discharged from a Perkins steam-gun ? 



If Mr. Scrope will recur to the par. 210 to 218 of my paper, he will find 

 that I do not reject any of the causes usually assigned for the irregularity, inter- 

 mittence, recuperation, change of position, etc., observed at volcanic vents ; 

 but I say that to account for these phenomena something more is wanted. 

 We must have some adequate cause for variation of the volcanic energy itself 

 at its focus. Those requisite conditions my theory supplies ; but it is wanting 

 to the older notion ; for whether the source of energy be derived from a 

 universal subterranean ocean of molten rock, or from Hopkins's fiery lakes, that 

 energy must be constant, subject only to an insensible secular decay. I do, 

 indeed, say that it is but a partial view to affirm that volcanic eruptions can act 

 as safety-valves to prevent earthquakes ; though it is needless I should occupy space 

 here by showing my grounds for that opinion. Mr. Scrope, however, wholly 

 mistakes my meaning when he goes on to say (page 34) : " Yet he himself argues 

 that his crushing mechanism for producing the heat at intervals, which gives rise 

 to volcanic eruptions, obviates the occurrence of paroxysmal 'Cataclysms' which 

 would probably destroy all living things upon the globe's surface. And what can 

 be meant in this connexion by ' Cataclysms ' but earthquakes of tremendous 

 violence?" What I do mean is made perfectly clear by the paragraph of my 

 paper, 221, which I commend to Mr. Scrope's re-perusal. Were there not 

 the self-adjusting mechanism by which the volcanic energy produced is just 

 sufficient at very short intervals to remove a proportionate amount of material 

 to enable our earth's crust to subside, but that such subsidence should be delayed 

 for long intervals, then at last the crust would become to such an extent un- 

 supported as to produce not only earthquakes, but such tremendous crushing 

 together and rending as must suddenly destroy the terrestrial regimen upon which 

 the existence of all organized life depends. 



Mr. Scrope concludes by saying, "On the whole I admit the plausibility 

 of Mr. Mallet's suggestion that some local development of heat must attend 

 the crushing and squeezing of irocky matter during the internal movements to 

 which their fractures and contortions, as well as the slaty cleavage of many, 

 prove them to have been subjected." This is cloudily expressed ; but if Mr. 

 Scrope means, as he must be understood to do, that these crushings are still 

 going on, then I am content to accept his admission, though expressed with a 

 minimum amount of approbation, because it in effect admits my entire theory. 

 All the objections in his remarks, numerous as they are, are mere questions of 

 "how much"; they are, in fact, mere cavillings with the numerical data upon 



