1S18.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



147 



sion of such matters through the substance of the contiguous strata, 

 as H-ell as for their local accumulation in fissures, or veins ; for it 

 was evident, that if these bodies were severally capable of under- 

 going volatilisation, at temperatures below that of their fusion, 

 the heat, which, originating in the intrusive rock, pervaded the 

 formations contiguous for a great distance around, would drive out 

 portions of all these substances, causing them to become dissemi- 

 nated throughout the latter, and, where fissures existed, to enter 

 in, and contribute to fill them. For this purpose, however, the 

 heat must be long continued, as well as of a certain intensity ; and 

 hence, whilst metallic veins were frequent in connection with 

 granite, they were entirely absent from sub-aerial lavas, owing to 

 the more rapidly cooling'that would take place in the latter, than 

 where the matter was thrown out under the sea, or at great depths 

 beneath the surface. Thus, according to this theory, the accumu- 

 lation of metallic matter in veins would have arisen, not from the 

 latter ha\ing been the original receptacles of whatever was disen- 

 gaged from the interior of the globe — for he agreed with Prof. 

 Bischoff, in considering that the idea of metallic, or indeed of any 

 description of veins, being injected in a state of fusion from below, 

 as trap and granite dykes were supposed to be, was encumbered 

 with insuperable difficulties — but owing to the subsequent action 

 of the heat upon the erupted matter, by which the metal might 

 have been slowly volatilised, and thus have found its way into the 

 fissures and cavities contiguous, when the principle of adhesive 

 affinity, described by Prof. Faraday in his " Memoir of the Limits 

 of Evaporation," would come into play; and no sooner was a thin 

 layer of metallic, or other body, collected along the walls of a 

 cavity, than the portions subsequently sublimated would be deter- 

 mined to the same point, until the whole cavity was filled up. 



The learned ])rofessor also alluded to Tilgman's discovery with 

 regard to the decomposing influence of steam at high temperatures, 

 wliich accounted for tlie decomposition of many rocks, and the for- 

 mation of combinations between the alkalies and fixed acids. 

 Various facts also proved that a certain exaltation of temperature 

 would favour the segregation and new combination of minerals, 

 though that was not essential. To influences of this kind such 

 formations as that of nodules of flint in chalk had been referred, 

 but he thought it more probable that the deposition of silica was 

 the result of the extraction of carbonic acid by the decomposition 

 of animal matter. 



He, therefore, suggested the importance of ascertaining by more 

 precise experiments what were the laws whicli regulated the va- 

 porisation of solids at temperatures below that at which they were 

 fusil)le. Assuming the truth of this principle, it threw considera- 

 ble light upon the alterations which contiguous strata underwent 

 from the intrusive rocks — for, the supposing a certain degree of 

 mobility to be produced by heat, witliout actual fusion, would en- 

 able us to understand these changes. The learned lecturer then 

 proceeded to discuss the diflficult question of dolomisation, which 

 he contended might be solved by a reference to the same princi- 

 ples, aided by analogous facts known to chemists, with respect to 

 carbon and other sul)stances. The whole question, however, ap- 

 peared to be oi)en to further inquiry, both as to the degree of vo- 

 latility possessed by magnesia and its several combinations, its 

 power of penetrating the substance of a calcareous rock, and com- 

 bining T\ ith its ingredients in atomic proportions — neither body 

 being in a state of absolute fluidity — its transmissibility to great 

 distances through an intervening mass of rock, and the circum- 

 stances which caused it to accumulate in certain sets of beds, and 

 to pass over others. Experiments should, likewise, be made as to 

 the changes which augitic rocks sustain under the influence of a 

 high temperature, and as to the possible disengagement from them 

 of magnesia under the circumstances supposed ; nor was chemical 

 research less called into request, for the purpose of enabling us to 

 explain such phenomena as were produced by igneous causes at 

 the present day, than for the elucidation of processes of higher 

 antiquity. When he reflected upon the assemblage of chemical 

 phenomena which presented themselves during the several phases 

 of volcanic action — the enormous and long-continued evolution of 

 carbonic acid — the inexhaustible supplies of sulphur, arising from 

 deposits, originally caused by the decomposition of sulphuretted 

 hydrogen — the volumes of steam and muriatic acid disengaged by 

 those volcanoes which were in a state of activity — the sublimations 

 of common salt, sal-ammoniac, &c., which generally accompanied 

 an eruption — tbe nitrogen gas evolved incessantly for centuries 

 from many thermal springs — when he saw these, and other results 

 of internal chemical action, come so prominently into view in every 

 part of the world where opportunities for studying the operations 

 of internal heat were presented, it did excite his surprise that 

 philosophers of high name should have rested content with a theory 



which professed to ascribe everything to the mere protrusion of 

 some of the fluid contents of the globe tlirough parts of its crus-t, 

 without regarding features so important, and apparently so essen- 

 tial, as those to which he had alluded. 



He thought that much was to be learned with respect to \'olca- 

 noes, by minute chemical examinations of the solid products 

 ejected, with a view of comparing their constitution one with 

 another, and of the gases and vapours evolved before, at the time, 

 and subsequently to, a volcanic crisis. Tlie learned lecturer then 

 referred to Prof. Abich's experiments with regard to felspar and 

 to the recent discoveries at Vesuvius, representing the evolution of 

 hydrogen from an active crater, and to the results which miglit be 

 expected from further discoveries. In tlie meantime, even with 

 our imperfect knowledge of these mysterious workings, we might 

 obtain glimpses of a beautiful system of compensation — of an 

 adaptation of means to an end — which struck the observer all the 

 more, when it was displayed, as in this case, in the midst of tliose 

 terrible manifestations of irresistible force, which the workings of 

 a volcanoe, or an earthquake, revealed. This was shown by the 

 useful purposes performed on the surface of the globe by the car- 

 bonic acid evolved from its interior, and was also iUustrated by the 

 occurrence of metals in veins, and the diffusion of phosphates in 

 minute quantities so generally through the strata. Had not this 

 been the case, the former would not have become known to us, 

 and the latter would not have been available for the nutrition of 

 plants. 



Such were a few of the facts to which he had been desirous of 

 directing attention, by way of inducement to his auditory to pur- 

 sue the science of geology with a frequent reference to chemical 

 principles; and he wished to impress upon those just entering 

 upon the study more particularly, the great truth, that in all kinds 

 of research, chemistry was to be regarded as the grammar to the 

 language of Nature — the key to unlock her most secret mysteries ; 

 and that those who were ambitious of following in tlie footsteps of 

 the great men who had adorned, and still adorn, that noble Insti- 

 tution, by fathoming the depths of some one of those sciences 

 which were there cultivated — nay, even those who, with humbler 

 aspirations, were content, like himself, to snatch a mere superficial 

 glance of several — would ever find it impossible to proceed with- 

 out its assistance. His own experience justified him in assuring 

 his auditory, that whether their chief interest might chance to lie 

 in physiology — vegetable or animal ; in scientific husbandry ; or in 

 those cosmical plienomena which presented themselves to the 

 explorer of mountainous regions — chemistry would suggest at 

 once the right principles for interpreting the facts observed, as 

 well as the soundest practical application that admitted of being 

 deduced from them. 



THE TIDES OF THE IRISH AND ENGLISH CHANNELS. 



Report of E.rperinients made on the Tides in tin Irish Sea ; ore 

 the similarity of the Tidal Phenomena of the Irish and Emjlish Chan- 

 nels ; and on the Importance of extending the Experiments round the 

 Land's End and vp the English Channel. By Captain F. W. 

 Beechey, R.N.— (Read at the Royal Society, March 9 and 16, 1S48). 



The author commences by stating, that the set of the tides in 

 the Irish Sea had always been misunderstood, owing to the dis- 

 position to associate the turn of the stream with the rise and fall 

 of the water on the shore. This misapprehension, in a channel 

 varying so much in its times of high water, could not fail to pro- 

 duce much mischief; and to this cause may be ascribed, in all pro- 

 bability, a large proportion of the wrecks in Carnarvon Bay. The 

 present inquiry has dispelled these errors, and furnished science 

 with new facts. It has shown that, notwithstanding the variety of 

 times of high water, the turn of the stream throughout the north 

 and south channels occurs at the same hour, and that this time 

 happens to coincide with the times of high and low water at More- 

 combe Bay, — a place remarkable as being the spot where the 

 streams coming round the opposite extremities of Ireland finally 

 unite. These experiments, taken in connection with those of the 

 Ordnance made at the suggestion of Professor Airy, show that there 

 are two spots in the Irish Sea, in one of which the stream runs 

 with considerable rapidity without there being any rise or fall of 

 the water, and in the other the water rises and falls without having 

 any perceptible stream ; and the same stream makes high and low 

 water in ditt'erent parts of the channel at the same time ; and that 

 during certain portions of the tide, the stream, opposing the wave, 



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