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THE EDINBURGH JOURNAL OF NATURAL HISTORY. 



to have belonged to Quadiumana, have appeared to us to be referable to other 

 groups." 



*' Though we are at present unable by any possibility to admit the extraordinary 

 fact of the assemblage in one locality of fossil remains belonging to animals so rigo- 

 rously limited in their geological boundaries as the true Apes, the Mnrmosets, and 

 the J'lakis ; yet the discovery of fossil bones belonging indubitably, as M. Lartt't has 

 clearly seen and pointed out, to ap Ape more nearly related to the Gibbons, which 

 are limited to the farthest parts of Asia, than to any other living species, does not the 

 less remain to be cons.dprcd as one of the most fortunate and unlooked for discoveries 

 which has been made in Palaeontology of late years ; and we propnse, in consequence, 

 that the Academy should continue to M. Lartet the encouragement which it has begun 

 to afford him, in order to facilitate his researches." — V Hermes, as quoted in Lou- 

 don s Magazine. 



Effect of Forests on the Sizk of River Currents. — The following obser- 

 vations, translated from VEcho du. Monde Savant, we extract from Loudon's Gar- 

 dener's Magazine. M. Bousingault, in a memoir recently presented to the Academy 

 of Sciences at Paris, has endeavoured to show the effects which the cleaiing away of 

 forests has upon the force and abundance of the river streams in a country. He 

 thinks that the current of water diminishes in jtroportion as the clearings extend; and 

 was led to take this view from observations made in America, especially in the lake 

 of Valencia in Venezuela, which has no outlet. This lake, in fact, diminished in 

 depth as fast a? the forests were grubbed up ; but as soon as, on account of political 

 troubles, the grubbing up ceased, the waters began to assume their primitive level. 

 Similar results have been furnished by the lake of Ubate. in New Grenada, and even 

 by those of Switzerland. 



M. Bousingault also thinks that clearing away the forests has a direct tendency to 

 diminish the quantity of rain. In the provinces of San Buenaventura, of Choco, and of 

 Esmeralda, w'hich are situate to the south of Panama, and where rains are almost con- 

 tinual, the soil is covered with thick forests, whilst towards Paita, beyond Tumbez, 

 the forests have disappeared, and rains may be said to be unknown. This want of 

 rain is in like manner observed in all the country near the desert of Sechara, and even 

 to Lima ; yet these two countries enjoy the same temperature, they present nearly 

 the same surface, and have a like position relatively to the mountains. 



RI. Arago remarks that a contrary result has been observed at Viviers, in the de- 

 partment of Ardeche, where the quantity of rain fallen has augmented since the 

 clearing of forests from the country. 



On the other hand, M. Deveze of Chabriol has come to the conclusion, from the 

 examination of several historical documents, that in the department of Cantal, in the 

 environs of Saint Fleur, there has been an abatement of temperature since the dis- 

 appearance of the forests. For example^ from the records of the 13th and 14th cen- 

 turies, it is proved that at this period the vine was cultivated on the slope of the hill 

 of Saint Fleur, and this culture will not succeed at present. The chestnut has also 

 disappeared from many of the cantons where it formerly flourished; and many villages 

 situated near the summits of mountains have been abandoned. It is also remarked 

 that, in this country, many streams have been dried up in consequence of the clearing 

 of the forests. 



DOLOMITES. 



On the Phenomena of DoLoaiisATioN, and the Transformation of Rocks 

 IN General, by M. Theodore Virlet. — The general question of the Transfor- 

 mation of Rocks is one of the newest and most important inquiries of Geology, th** 

 solution of which ought to furnish us with the means of making rapid progress,, in 

 the study of the composition of rocks, and lead to the elucidation of a multitude of 

 isolated facts, hitherto considered as inexplicable. 



While describing to the Geological Society of France, some years ago, the modi- 

 fications which presented themselves in a bed of hematitic iron, which I had an op- 

 portunity of inspecting, near Sargans, in the Canton of St Gall, Switzerland, I w^as 

 led by the recollection of numerous analogical facts falling under my notice, and men- 

 tioned in my account of the Geology of Greece, to regard the phenomena of the 

 transformation of rocks under two different points of view, and to separate the modified 

 rocks into two very distinct classes. 



1. Such as have been modified, whether by the prolonged action of heat, or by 

 that of electro-chemical agents, or by both of these causes united, which have alterec' 

 combinations or primitive arrangement of the molecules in relation to each other. 



2. Rocks which have been modified by chemical actions and reactions, with the 

 assistance of foreign agents (such as the gases), which acted directly upon them, 

 and changed their primitive nature. It is in this class the Dolomite, or Magnesian 

 Limestone, should be arranged. 



The first manner of regarding the modification of rocks, which was originally sug- 

 gested by me, serves to explain how certain beds, placed in the midst of other beds, 

 may be more modified than the latter, or may even undergo a complete modification, 

 without the others, whether they were in contact, or even formed the lower part of 

 the same deposit, experiencing any sensible change in their original state, and that 

 without any of the beds being confounded with each other. The opinion which 1 

 advance on this subject results as much from my own observations as from the 

 manner in which 1 regard the first sandy deposits, as being formed at a period when 

 the waters began to condense on the surface of the earth, and although many may 

 consider it as somewhat heretical, 1 have no doubt that it will soon be admitted by 

 all accurate observers ; namely, that all stratified rocks, without excepting gneiss, 

 the mica slates, or clay-slates, &,c. have been originally rocks of sediment, formed by 

 mechanical aggregation, and that they have acquired the crystalline characters which 

 now distinguish them by a series of modifications, which they have undergone pos- 

 teriorly to their being deposited. 



It is conceived, on the contrary, according to the second kind of modification of 

 rocks, that in the greater number of cases, all the beds are confounded in such a 

 manner as to present a single mass without distinct stratification ; such, for example, as 

 Dolomite, certain deposits of sandstone and clay transformed into jaspers, or trachytes, 

 or porphyries, and other rocks which I have had occasion to enumerate, for the chemical 

 agents, by penetrating across a certain number of beds, or even the entire mass, have 



separated apart of the elements of the original rocks and substituted others, or ejse 

 have formed new combinations, and finally united the whole mass of the deposit. It 

 is to these considerations th;Lt I wish chiefly to direct attention, as they have re- 

 ference to the phenomena of Dolomisation. 



I do not dispute, that there are Dolomites which should be called primitive, what- 

 ever maybe their geological age; that is to say, which were the result of simultaneous 

 deposits of carbonate of lime and of magnesia, for magnesia was at least as abundant 

 in nature as lime, particularly at the time when the old deposits were formed. These 

 primitive Dolomites, however, always present a distinctive character in being 

 regularly stratified, like the other rocks to which they may be found subordinate; 

 while the Dolomites of which I now speak, and which I shall designate Dolomites of 

 Transmutation (such as are described by M. de Buch as occurring among the 

 Alps, and many others which I could mention), are without stratification, presenting 

 irregular masses, combined with other characters, which individuals accustomed to 

 observe modified rocks can seldom mistake. No one who has visited the Dolomites 

 of the Alps can entertain any doubt of the reality of the phenomenon of Dolomisation, 

 however difficult the explanation of it may at first appear, since chemistry teaches us 

 that carbonate of magnesia is not volatile, or that it is decomposed at a red heat, an 

 objection that has not been urged by M. Thenard. It was in fact these consider- 

 ations that caused me to be among the first to publish my doubts on the subject, at 

 a time when no one undertook to ascertain, by chemical analysis, that the parts of 

 the deposit which had not been modified were not equally magnesian, that is, did 

 not form beds of primitive Dolomite, a circumstance vvhii-^h would have reduced the 

 phenomenon of the change of Limestones into Dolomite to a simple phenomenon of 

 modified crystallization, analogous to that, for example, which has determined the 

 change of the compact Jura Limestone of Carrara, and that of the compact chalks 

 of some parts of the Pyrenees, into granular Limestones or Statuary Marble. One 

 of my friends, M. Des Genevez, who possessed a very extensive knowledge of 

 chemistrv, and whose early scientific works afford so much reason to lament his 

 premature death, has unhappily been lost to the sciences before publishing the results 

 of his chemical researches on Dolomisation. These, he has many times assured me, 

 had demonstrated to him that there existed an insensible passage from beds of un- 

 altered carbonate of hme to dolomite or double carbonate of lime and magnesia. 

 Thus, the transformation yf certain calcareous rocks into dolomite, posteriorly to their 

 formation, appears to me to be a well established phenomenon, and requires, in my 

 opinion, only to be properly explained, in order to be admitted by all. 



Who does not know how many facts, perhaps among the most difficult to compre- 

 hend previously, have already been explained by the excellent researches of jVL 

 Becquerel, in electrical chemistry, and the important labours of M. Fournet, re- 

 garding the formation of veins? Numerous other facts, although not yet fully 

 explained, have been brought forward and admitted without dispute. For example, 

 I have proved that the Emery of Naxos comes from veins, and consequently had been, 

 formed, like the greater number of specular iron ores, by means of volatilization and 

 sublimation ; yet the corundum and oxide of iron, the mixture of which constitutes 

 Emery, are not more volatile than the carbonate of magnesia, which forms the sub- 

 ject of dispute. 



Since our chemical knowledge, then, does not always enable us to explain the phe- 

 nomena whose existence we can prove, does it follow that we ought to call them in 

 question? Has Nature no mode of acting which surpasses our knowledge? And 

 -could she not proceed, for instance, by means of double chemical decomposition? 

 On this supposition the phenomena will admit of easy explanation. It is well known 

 that all the muriates are volatile, or at least susceptible of sublimation. Magnesia 

 mi"ht then easily reach the state of a muriate, and occasion the formation of a solu- 

 ble hydrochlorate of lime, which would be carried oft" by the infiltration of water; 

 while the magnesia, on the contrary, would be combined with that portion of the car- 

 bonic acid set at liberty, and would thus serve to form the double carbonate of mag- 

 nesia and of lime, which constitutes dolomite, properly so called. In this there is 

 ceitainlv nothing inadmissible or contrary to reason, inasmuch as the hydrochloric 

 acid gas Is one of the gases most frequently disengaged from volcanoes; and the mu- 

 riates ought to have been disengaged more abundantly in former times, if we admit, 

 with geologists of the modern school, that the immense deposits of rock-salt which 

 exist in saliferous formations, are deposited by volatilization in the midst of the strata 

 which they penetrate. 



I am therefore of opinion, that the modifications of rocks of the second class may 

 henceforth be explained by means of double decomposition — a process which has 

 enabled one of my friends, M. Aime, to produce in the laboratory crystallized specu- 

 lar iron ore, analogous to that of the island of Elba, as well as pure iron equally well 



crystallized a substance hitherto unknown to mineralogists ; whence I conclude that 



the time is not perhaps far distant when we shall be able to produce with ease all the 

 species of precious stones, without even excepting the diamond. 



Fossil Footsteps in Sandstone and Greywacke. — Professor Hitchcock has 

 discovered in the valley of the Connecticut River, the imprints of what he considers 

 fourteen new species. Some bear' so near a resemblance to the feet of Uving Saurians, 

 that they have been denominated Sauriodicknites. The Professor says, " I have no 

 certain evidence as yet that any of these impressions were made by four-footed animals, 

 although, in respect to two or three species, I have strong suspicions that such was the 

 fact. I have sometimes thought they might have been made by Pterodactyles, yet 

 they have in general fewer toes than those described by Cuvier and Buckland. Within 

 a few weeks past, I have found on the flag-stones, in the city of New York, some 

 marks, which I suspect were made by the feet of a didactylous quadi-uped, which, 

 like the Marsupialia, moved by leaps. The rock is slaty greywacke, from the banks 

 of the Hudson, between Albany and the Highlands. "—Sii/iman's Journal. 



Edinburgh: Published for the Proprietor, at the Office, No. 13, Hill Stteet. 

 London: Smith, Elder, and Co., 65, CornhiU. Glasgow and the West of 

 Scotland: John Smith and Son; and John Macleod. Dublin: George 

 YoDNG. Paris: J. B. Ballikre, Ruede I'Ecole de Medecine, No. J3bis. 



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