« PreviousContinue »
neighbourhood of Cochin, and to comply publicly with the archbishop's wishes.
The archdeacon, in the hope that his compliance would prevent the visit with which Menezes threatened his churches, promised to do all that was required of him. He attended on the day appointed, and being seated on a chair prepared for him in the presence of the Governor of Cochin, accompanied by many, both of the clergy and laity, a Portuguese priest read to him the confession of Faith in Portuguese, demanding of him if he believed all that was therein contained. The archdeacon, who did not understand Portuguese, answered in the affirmative without hesitation ; and the same when they asked if he acknowledged the Pope as the head of the church and the archbishop of Goa as his superior. The Portuguese (adds La Croze from whom this whole narrative is taken) received this confession with great expressions of joy, but the Jesuits, who were within hearing, judged very differently. Menezes who received from Vaipicotta a full account of the whole transaction, resolved, notwithstanding the wars of Malabar and all the other inconveniences that oppposed him to visit the churches of Șt. Thomas without delay and to reduce them finally to the obedience of the Holy See. The narrative of that expedition must be reserved for a subsequent communication.
The Editor of Journal
of the Madras
Literary Society. IV.-As frequent notices have been made regarding the Earthquake, which occurred on the 26th of last August, the vibrations of which were experienced over an extensive range of country in Bengal, and as several queries have been submitted for consideration as to the cause of earthquakes generally and locally, I have been induced with the view of contributing my mite, in support of the Madras Journal, to offer the following brief outline, in which no profession is made of furnishing any original illustrations, my only object being to arrange various established truths drawn from the latest authentic sources of geological knowledge, in a condensed form adapted to the limits of a periodical publication.
B. W. WRIGHT,
Asst. Surg. 8th Regt. N. I. Vizianagram, 28th Octr. 1833.
The theory of the subterranean movements being so intimately blended with that of the whole terrestrial system, it appears advisable to consult various works on the formation and revolutions of the earth, ancient and modern. In these it will be found that a vast accession of knowledge, has been gained from modern physical and geological discoveries, geologists having of late years explored many mysteries, the structure of the earth being surveyed minutely and in detail, the organic inscriptions of its different strata being carefully examined, and comparisons made, facts have been ascertained, beyond the reach of former philosophers, each of whom had a creed of his own considered supreme, their system being essentially dogmatic, having entirely disregarded the Mosaic account of the creation, the only certain foundation to build upon.
Werner and Hutton are two of the latest and most celebrated of these philosophers, being the leaders of the rival factions of the Vulcanists and Neptionists so called from their different definitions of the terrestrial system. Werner considering that the globe was anciently covered by a vast solution, differing from our existing seas, and that this chaotic ocean contained the elements of the primitive lands, whilst Hutton attributed every thing to the agency of internal fire; his theory is the most elaborate, and comprehensive, that has hitherto appeared ; giving a general abstract of it here would however exceed the bounds allotted to this disquisition, the defects and inconsistences of both systems have of late years been ably exposed by Lyall, Ure, and many other practical naturalists. Ure after criticising, both cosmological systems, compliments the authors on having decked them out in very technical language although he winds up this eulogium with stating that their theories are almost as fantastical and extravagant as that of some of the an. cient philosophers of the Tonic, and Attic, schools. On perusing the geological works of Smith, Maccullock, Lyall, Ure, and other late writers, it will be found that a new school has arisen, in which speculative and dogmatic systems are entirely discountenanced. In Lyall's account of the geological society of London, he states “ that the system in vogue is to multiply and record observations, and patiently await the result of some future period, it being their favourite maxim, that the time is not yet come for a generat system of geology ; but that all must be content for many years, to be exclusively employed in furnishing materials for future generations; by acting up to their principles with consistency, he says, that they have in a few years disarmed prejudice, and rescued the science from the imputation of being a dangerous or at least a
French naturalists, have also of late years, by the application of the history of organic remains, to the science of geology, given many enlarged views regarding the former changes of the earth; comparisons having been made between ancient and modern fossil specimens, and inferences drawn with regard to their habits.
To proceed however in the more immediate investigation of earthquakes; formerly peculiar states of the atmosphere were considered productive, and prognostic of these convulsions; there is generally allowed to be an intimate connexion, but as Mitchell has remarked, “ it is more probable that the air should be affected by the causes of the earthquakes, than that the earth should be affected in so extraordinary a manner, and to so great a depth by a cause residing in the air.”
It is however the general opinion of all late authorities, that earthquakes, and volcanoes are intimately blended, being the effects of the same agents, although they give rise to different phenomena on the surface of the globe. I shall therefore first give some account of Sir Humphry Davy's theory of volcanic actions; which is generally allowed to be the most correct and satisfactory. From thermometrical experiments on the temperature of mines, and hot water springs, it has been shewn that the interior of the globe, possesses a high temperature, which in some degrée simplifies the problem of volcanic fires. Sir, H Davy says, “ that on the hypothesis of a chemical cause for volcanic fires, and reasoning from known facts there appears to be no other adequate source than the oxydation of the metals, which form the basis of the earths and alkalis. He considers, that these from their great affinity to oxygen, could not exist on the surface of the earth, but only in the interior of the globe, and that volcanic fires are occasioned, whenever these are exposed in subterranean cavities to the action of air and water." On examining a stream of lava, issuing from Vesuvius, he ascer. tained that there was no combustion going on at the moment of its exit from the mountain, on lifting up some of it in an iron ladle it did not ignite more vividly, on being exposed to the air, some of it was poured into a glass bottle containing silicious sand at the bottom, a ground stopper was closed at the moment, and the bottle was found to contain when afterwards examined by the test of nitrous gas as large a proportion of oxygen as common air ; when melted nitre was thrown over the lava, it fused from the heat, but there was not the least increase of deflagration, to indicate
the presence of combustible matter ; various other experiments were followed by the same inferences upon another occasion, when fame and steam issued from the crater, there was no indication of carbon. I have however mentioned sufficient to prove, that the causes anciently assigned for volcanic fires, are proved by Sir H. Davy to be fallaci- . ous, the most current of these was the combustion of mineral coal, this he says “is most inadequate, for however large the strata of pit coal might be, its combustion under the surface could never produce intense heat, the production of carbonic acid gas, would impede the process and if this cause existed, carbonaceous matter would be found in lava. In England, there is an instance of strata of pit coal having been long burning, but the only result was, baked clay not in any way resembling iava, the action of sulphur upon iron has also been assigned as a reason, but were this the case sulphate of iron would be the chief product of the volcanics, “Sir H. Davy therefore assigns these phenomena to chemical causes, the products of volcanoes giving an idea of the substances primarily active ; these are found to contain mixtures of the earths and alkalis in an oxydated and fused state from intense ignition, water and saline substances are also found, such as may be furnished by the sea and air but altered in such a manner, as may be expected from the formation of fixed oxidigied matter. He moreover states, as a reason, why the combustion is not increased, when the volcanic productions pass into the atmosphere, that volcanic fires take place in immense subterranean cavities, and that the access of the air to the acting substances occurs long before they reach the day, lava being the refuse of combustion below, Lyall and several other practical naturalists support these opinions, observing that earthquakes are generally attended and preceded by heavy torrents of rain inundating contiguous regions, water being supposed to percolate and descend by fissures to those cavities accounting in some degree for the prevalence of earthquakes and valcanoes in Islands, and in countries, bordering on the sea. Before the eruption of the hot springs in Iceland, the ground is always agitated, and if the vapours which are condensed in these small cavities are capable of agitating the ground to any extent, what may be expected when they are confined below in extensive subterranean cavities. The intensity of the heat in these regions, and the density of the air from the immense
pressure from above can only be imagined when it is known that limestone melts without giving off its carbonic acid under a pressure of 1700 feet of sea which only cor
responds with 600 of liquid lava as proved by Sir James Hall. That immense subterranean cavities exist there can be no reason to doubt, there being apparent communications at great distances between different volcanoes. Ure mentions“ that the limestone caverns of Carniola contain many hundred thousand feet of cubic air, which he says shews the extent to which subterranean cavities may exist even in common rocks, and the deeper is the excavation, the denser is the air, and the fitter for combustion." Lyall suggests that the circulation of heat from the interior to the surface is probably regulated like that of water, from the surface to the sea, in such a manner that it is only, when some obstruction occurs that the usual repose of nature is broken.” In order next to prove the intimate affinity of volcanoes and earthquakes, it will be found, that the former are distributed over vast tracts, and there is plentiful evidence that subterranean fires are continually at work in the spaces between. Earthquakes being of frequent occurrence, hot springs being distributed at intervals impregnated with the same mineral matters as are discharged by volcanoes, and gaseous vapours being discharged plentifully from the soil, several writers have of late years declared, that the energy of subterranean fires has considerably abated, several volcanoes having become dormant; but it would be difficult however to define a tine in which a volcano may be said to be extinct, as there are instances on record of a recurrence of eruption after a dormant state of several centuries in the same volcano. In continuance of the proof of the intimate relation of earthquakes, and volcanoes, the region of the Andes is said to be one of the best defined there being an uninterrupted line of volcanic vents, in almost every degree of latitude from the 46 south to the 27 north ; in these different provinces hot springs are numerous and mineral waters of various kinds, a year seldom passes without slight shocks of earthquakes, and once in a century convulsions occur by which continuous tracts of land have been raised from one to twenty feet above their former level, many extensive vallies in this chain of mountains, have been filled up with volcanic products; the volcano of Jorullo, which is in about the centre of the range is 40 leagues distant from the sea which is considered important as it shews that proximity to the sea, is not a necessary condition, though the general characteristic of volcanoes; besides the volcanic range of Andes, there are others of even greater extent mentioned, of which a discription would occupy too great a space. The volcanic bands of the Molucca and Sunda Islands, are the nearest however to the cuntinent of