.Sept. 14, 1 8380 



SCIENTIFIC NEWS. 



289 



.Vesuvius, and others of the same type, cannot but be struck with 

 the fact that the enormous evolution of watery and other vapours 

 does not suffice to reduce the temperature of the magma to the point 

 of solidification. 



By carefully following the details of the varying activity of the 

 above-mentioned volcanos, which we will choose as our types, the 

 matter becomes comprehensible. There is little doubt that all 

 igneous magmas are oiigirally in a vitreous condition, and that the 

 passage from that stale to a crystalline one must be accompanied by 

 the evolution of an enormous amount of heat, just as occurs in the 

 passage from the solid slate of ice to the liquid water. Were the 

 magma composed of a single chemical compound, we should ex- 

 pect that it would remain at a fixed temperature from the com- 

 mencement of crystallisation to the complete solidification as the 

 result of that process. This would not be the case in the lava in a 

 volcanic chimney in which we should expect that the temperature 

 would fall by steps, remaining fixed as long as any definite mineral 

 species was crystallising, and would then drop to the crystallising 

 temperature of the next species, again remaining for a certain time 

 fixed. What these temperatures should be we do not know until 

 the crystallising temperature of each rock-forming species is known. 

 It must be remarked that the simple fusion point of any mineral is 

 no indication of the temperature of the crystallising of a given 

 mineral from a magma ; for, in the former case we have to deal with 

 a simple physical process, whereas in the latter it is often a chemical 

 one. This is illustrated well in the case of orthoclase and augite, 

 which both crystallise before leucite, which can only be explained 

 by a chemical reaction taking place in the magma. 



This process I take to be dependent upon a magma open to the 

 atmosphere, by which the alkaline chlorides break up, the HO being 

 liberated and the free alkalies combining with the silica and alumina 

 of the basic iron glass. Part of the iron separates as magnetite and 

 part combines with the HO and escapes in the vapour as chloride, 

 always accompanied by some of the alkaline chlorides. 



In fact, it seems an almost impossible task, the determining 

 theoretically or even practically the temperature of solidification of a 

 lava. 



However, a clear comprehension of what has been said demon- 

 strates how the supply of heat is kept up for a long time in the 

 volcanic chimney, and the varying activity resulting therefrom. We 

 have good reason to suppose that in our type ot volcanoes there 

 comes to the surface a uniform quantity of magma in a given time, 

 although the extrusion may be more or less rhythmical, due to tidal 

 and other agencies. Let us suppose that the magma has been so 

 long simmering in the chimney that by volatilisation of steam, etc., 

 it begins to become pasty. In that condition the escapeof vapourfiom 

 the lower part of the magma in the chimney cannot go on, and con- 

 sequently the fall of temperature is arrested although crystallisation 

 may go on for some time, so that the temperature of the lava rises. 

 Meanwhile more water is being dissolved or taken up by the magma, 

 and, in consequence of this and the rise of temperature, the tension 

 of the magma increases until it overcomes the resistance of the pasty 

 magma choking the upper part of the chimney. Then occurs a 

 more or less strong paroxysmal eruption, in which, from the excess 

 of water and the higher temperature there will result a tendency to 

 the issue of the magma in a fragmentary condition, and this will 

 approach more or less the scoriaceous or e;en pumiceous character. 

 This is what is constantly occurring at Stromboli and even at 

 Vesuvius, but in the latter it is much modified by the lateral oozing 

 of lava, the effect of which I propose to treat of elsewhere. 



In fine, we must conclude that the calorific capacity of the original 

 vitreous magma must be very great, although its temperature may 

 not be very high, and that its heat energy under favourable condi- 

 tions may keep up the temperature for a long time. This would be 

 the case in a volcanic chimney when solidification was taking place 

 by crystallisation instead of cooling as a glass — a similar condition, 

 in fact, to what we observe in the solidification of melted sulphur. 



The same author then read a Note on a Mass containing 

 Metallic Iron found on Vesuvius. 



He also contributed a Note on the Occu'rence of Leucite at Etna. 



Professor E. W. Clay pole, B.A., D.Sc. (Lond ), F.G.S., of 

 Bochtel College, Akron, Ohio, U.S.A., contributed a Note on Some 

 Recent Investigations into the Condition of the Interior of the Earth. 

 The difficulty of this great problem in geology was referred to as a 

 reason for the slow progress made towards its complete solution, 

 and indirect nature of the evidence was also quoted as a source of 

 uncertainty. The chief element upon which reliance can be ploced 

 is the now seldom disputed datum that the earth must in all these 

 inquiries be regarded as a heated body in cold space subject to laws of 

 radiation as yet imperfectly understood. Reference was then made 

 to the recent investigations of Mr. C. Darwin, Mr. T. M. Read, 

 the Rev. A. Fisher, and Professor G. Darwin, claiming to prove that 

 the following deductions from this datum have been established. 



(a) That below 400 miles the cooling and consequently the con- 

 traction are imperceptible. 



(<5) That the cooling and consequently the contraction reach their 

 maximum at the depth of 72 miles. 



(c) That at the depth of five miles the contraction from cooling 

 exactly equals the diminution of space due to the descent of the 

 shell ensuing from the total vertical contraction of all the layers. 



This layer, at the depth of five miles, has therefore been termed 

 " the layer of no strain,'' being liable neither to extension nor com- 

 pression, because the space is exactly sufficient for its diminished 

 bulk. The layer of no strain is placed by one of the authors above 

 named at the depth of five miles, and in a neutral zone between the 

 bent and crushed strata above, and the compressed and horizontally 

 extended strata below it. It is consequently impossible that any 

 disturbance can occur in the layer of no strain. 



Yet in some parts of the earth, and notoriously in the Appalachian 

 region of North America, strata have been forced up from a depth 

 greatly exceeding this limit. Beds are now exposed, which at the 

 time of their folding, lay fully eight miles below the surface, and 

 must therefore have been far below this neutral zone, which was 

 then (at the end of the pa'feozoic age) less than five miles deep. 

 Similar facts might be adduced from other parts of the world, and 

 it is therefore difficult to avoid the conclusion that the layer in 

 question has been placed too near the surface, though of the actual 

 existence of such a zone after a careful study of these investigations 

 scarcely a doubt can be entertained. The Professor concluded by 

 pointing out that this theory would limit the depth and origin of 

 earthquakes to a five-mile depth. 



The President said the subject was one of exceeding difficulty, 

 and exceeding interest, and it was a subject, moreover, upon which 

 hardly any two observers were likely to come to exactly the same 

 conclusion. To the point put before them by Professor Claypole 

 they must really devote some discussion. Geologists were plain 

 folk ; they required evidence put clearly and plainly to the front, 

 and he thought there was really no evidence of any such divisions. 



The Rev. E. Hill, M.A., F.G.S., who pointed out that mathe- 

 maticians (the authors of the theory put forward by Professor 

 Claypole) obtained their deductions from hypotheses, declined to 

 discuss that question, but confined himself to the question of volcanic 

 agency. There were, he said, several theories of volcanic action. 

 There was the theory of the crushing process ; there was that of 

 the gradual percolation of water to the heated depths ; there was 

 that of the sudden intrusion of water into the heated core ; and 

 there was the later one, which had much to say for itself, of heated 

 gas gradually forcing its way out from the central nucleus. Some 

 facts seemed to point in favour of one hypothesis and some in favour 

 of another. For instance, the description which Miss Bird gave 

 of a volcano in one of the Sandwich Islands, as that of a constant 

 boiling going on, seemed to be best explained by the theory of 

 heated gas ; or, again, the fearful eruption which, in New Zealand, 

 destroyed those wonders of the world, the Pink and White Terraces, 

 seemed much more clearly to be attributed to the sudden intrusion 

 of the waters of the lake into the heated central mass. Other obser- 

 vations pointed to other causes, and he was inclined to think they 

 often made the mistake when they saw one phenomenon of imme- 

 diately considering it must be due to one cause, whereas he strongly 

 suspected that in these matters several causes were at work. 



Dr. Irving, after dealing with the presence of flame in vol- 

 canic eruptions, pointed out that the architecture of the earth's 

 crust was such as to throw serious difficulties in the way of Professor 

 Claypole's theory of a zone of "no strain," especially in view of 

 the fact that in earlier periods such a zone must have been much 

 nearer the surface. 



Mr. Stanley criticised the mathematical calculation by which 

 the theory had been arrived at. 



Mr. Beaumont, Mr. W. White, and Mr. Fergusson 

 followed. 



The Rev. F. Howlett, F.R.A.S., said he was astonished to 

 hear the statement made by the mathematicians that at the depth of 

 4.C0 miles the central mass was incapable of further cooling. If 

 that were so what became of the theories and functions of the laws 

 of convection currents of temperature ? He was utterly incapable 

 of comprehending how such a state of things could possibly be 

 arrived at. 



The President followed with a vigorous onslaught on the " no 

 strain zone " theory. They had already heard some objections which, 

 to his mind, were insuperable objections — that by the last speaker 

 particularly. It was asserted that the temperature of the earth be- 

 yond the 400 miles limit would remain the same for ever and ever ! 

 That was a hypothesis which they could not for one moment enter- 

 tain, unless they had most ample and conclusive proof. Now for 

 this five-mile line — the line of " no strain." Now if there ever had 

 been, at a depth of between one and five miles, such a layer as that 



