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AUVEUGXE. 



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gneisa, which in iU turn graduate* into mica-late, we may infer that 

 part at least of the mum of granite was contemporaneous with the 

 inferior stratified rock, of the district Be thu a* it may, the bed. of 

 gneiss, mica-slate, and others of the aame clam, are sometimes highly 

 inclined and contorted, at may be observed near Meiiat, on the Sioule, 

 in the north of the department of Puy-de-Dome, showing that they 

 hare been acted on by aome powerful force ; but aa these beds may 

 have been exposed to the action of many powerful forces during the 

 aerie* of age* which have elapsed since their production, we cannot, 

 without bettor evidence than we possess, readily fix on the geological 

 epoch when the gneiss and mica-date* were first thrown out of their 

 original positions. 



Above theee primary rook* are found others that must have been 

 formed at periods separated from each other by considerable intervals 

 of time, since many rock* necessary to complete the series of European 

 deposit*, are wanting between them. Finally, uumerou* volcanoes, 

 now extinct, poured forth an abundance of igneous products, which, 

 though comparatively recent, have covered the remains of animals 

 that have disappeared from the surface of our planet The rocks 

 which in the order of relative antiquity succeed the inferior stratified 

 and granitic rocks above noticed, are referred, from the vegetable 

 remain* detected in them, to the same age as the coal-measure* of 

 Great Britain. Their general mineralogical characters are also simi- 

 lar, beds of coal being associated with shales, sandstone*, and con- 

 glomerates ; the whole appear* to be the result of drifted vegetable 

 matter, and of detritus from pre-existing rocks accumulated in unequal 

 quantities and at unequal intervals of time in particular situations. 

 The extent to which these carboniferous rocks once covered the gra- 

 nitic area of Central France cannot be conjectured, owing to the various 

 geological changes to which the surface of the country has been 

 exposed ; but we may infer from the general characters of the scattered 

 portions now observed that the coal-measures were at one period more 

 extensively distributed over Central France than we now find them. 

 The manner in which these carboniferous rocks occur would lead us 

 to suppose that they had been deposited upon an uneven surface of 

 pre-existing rocks, and that the time necessary for the accumulation 

 of the vegetable matter must have been considerable ; since the coal- 

 bed*, though they vary considerably in this respect, sometimes attain 

 twenty or thirty yards in thickness. As the fossil plants discovered 

 in these deposit* do not afford any evidence of distant or violent 

 transport, we may consider that dry land existed in the area now 

 occupied by Central France at the epoch of the carboniferous group. 



A long interval of time appears to have elapsed, judging at least 

 from the rock* now found in Auvergne, before any other deposits 

 were formed in this part of the European area. During the various 

 change* to which it ha* been exposed, rocks may indeed have been 

 produced, and have been subsequently removed ; but as no traces of 

 such product* are now visible, the evidence i in favour of conditions 

 unsuited to the formation of rocks in this district during a considerable 

 geological period, extending from the epoch of the carboniferous group 

 to that of the cretaceous group inclusive. If Central France ha* been 

 elevated above the general level of the ocean from the time of the 

 coal-measure* to the present day, a* we might infer from the total 

 bsenee of rock* with marine remain*, conditions would aoessarily 

 be unfavourable to the production of any abundant equivalents of 

 those thick and numerous deposits of transported matter which occur 

 in various parts of Europe, and which are inferred form their organic 

 content, to have been formed in a sea. We should however expect to 

 discover trace* of deposit* effected in lakes, by the sides of rivers, and 

 in other situation* where transported detritus and calcareous matter 

 precipitated from water could find place* of rest Conditions appear, 

 however, to have been unfavourable for any accumulation of such 

 deposits in sufficient abundance to leave trace* of their existence, until 

 the snpracreUceoua epoch, when large lakes were filled with detritus 

 and calcareous matter. 



The supracretaoeou* lacustrine deposits of Auvergne have been 

 divided into three portions : 1. An inferior accumulation of sand- 

 stone* and red and variegated marls ; the former being the lowest 

 In these are discovered the remains of a quadruped, of a few small 

 reptiles, and the impressions of dicotyledonous plants. 2. A central 

 accumulation of marls, limestones, and gypsum, in which are found the 

 exuvue of the Palavtlurium, AnoploOurium, AnOuraeotMerium, a small 

 pachydermatous creature, the crocodile, tortoise, some small reptiles, 

 and of birds analagou* to the genus Amu; to which may be added the 

 eggs of birds, sometimes well preserved. 3. A superior deposit of 

 limestone and marl, containing an abundance of the Induita t*b*lata, 

 Cypni Palm, (iyngtmttrt, Putamidti, Helix, Ac. The remains of nume- 

 rous rertebrated animals are discovered in it ; among which there are 

 three specie* of rhinoceros, two ruminant, analogous to the genus 

 ATiMcAw, animals of the genera C'anii, Petit, Ac. The only portion of 

 this mas* of deposited matter of which the relative age has been 

 doubted coosuU of certain sandstones, constituting the base of the 

 whole, and termed arkoee, a name also given to a rock discovered in 

 a situation intermediate between the lisa and the granitic district of 

 Central France, and therefore of much greater antiquity than the 

 lacustrine deposit under consideration. The mere mineralogical 

 resemblance of the two rocks is of little importance, since they are 

 both formed of detrital matter derived from the granitic district itself, 



and which has afforded similar silt, sand, and gravel at various geo- 

 logical epochs; so that rocks formed at different periods may be 

 separated from the granitic mass beneath by similar sandstone*. 



The lakes, for there would appear to have been several, in wliirh 

 this mass of limestone and marl was deposited, must have been deep, 

 since the thickness of the lacustrine formations of Auvergne has been 

 estimated at 800 or 1000 feet in some places. The beds of which it 

 is composed vary from 2 or 8 inches to 6 feet in depth, some of the 

 lamina: being exceedingly thin ; and the whole taken generally pre- 

 senting the appearance of slow and tranquil deposition. As the 

 remains of the mammiferous animals detected in the upper jiortion 

 do not correspond with those discovered in the lower part of these 

 beds, we may infer that a considerable change in the terrestrial 

 animal life of the district was effected even during the time thut thu 

 various deposits were made in the same lakes. 



Subsequently to the production of the greater propoi 'ion of the 

 lacustrine rocks noticed above, the surface of the country '.."as broken 

 up, and volcanic products ejected in great abundance. In ihe depart- 

 ment of Cantal, which is part of Auvergne, no evidence has been 

 adduced to show that any portion of the lacustrine rocks was pro- 

 duced after the volcanic eruptions commenced ; it is otherwise 

 however, with the northern part of the district, for the lacustrine 

 deposits of the Limague had not terminated before the volcanoes 

 burst forth in that direction, as may be seen at the hill of Oergovia, 

 and two or three other places in the vicinity of Clermont-Ferrand. 



The volcanic products are extremely various ; some appearing like 

 the older rocks melted by heat beneath and thrown up, while others 

 seem to have been derived from matter deeper seated. The two 

 groups of the Cantal nnd the Mouta-Dor are remarkable for a certain 

 general resemblance to each other, consisting principally of trachytes 

 and basalt; the former having been as a whole lirst thrown up, 

 dislocating the lacrustine rucks where they opposed their ejection, aa 

 may be seen in the Cantal between Aurillac and Murat, particularly 

 from the village of St-Roque to Polminhac. Large fragments of 

 lacustrine limestone (from 40 to 60 feet in diameter) are iucliuli il 

 among the trachytic conglomerate near Oiou. The trachytic rocks of 

 Cantal have not been produced at a single eruption, but appear to 

 have been formed at distinct intervals of time, judging at least from 

 the repetition of thu beds. Dykes of trachytes cut through the 

 principal masses, as may be observed near Ferval, and near the 

 source of the Ccr ; and it is inferred that the trachytic eruptions of 

 Cautal ceased before the basaltic matter was poured forth, since the 

 truchytic dykes do not traverse the basalt The latter and its con- 

 glomerates cover the trachyte in a nearly continuous mass, broken 

 only by the radiating lines of valley and the central part of the group, 

 where the inferior rocks are exposed to view. The Plomb de Cantal, 

 which is the highest part of the group, attaining an elevation : 

 feet above the sea, is formed of a small patch of basalt This rock 

 also occurs in dykes traversing the trachytic masses, sometimes 

 spreading out over their upper surfaces ; the Puys- Violent (8282 feet 

 above the sea) is thus formed, and it is worthy of remark that the 

 basaltic dykes of this mountain keep a very constant direction from 

 8. 10 E. to N. 10 W. Like the trachytio rocks, the basalts of 

 Cantal do not appear to have been formed at a single eruption, since 

 they constitute several bed*. In the environs of the Puys-Violcut, 

 and on the flanks of the Vallce-du-Mars, two beds of basalt are 

 separated by a thick accumulation of basaltic conglomerate, the 

 lowest bed of basalt resting on trachytic tuff. Messrs. Dufrenoy and 

 Kliu de Beaumont consider that the clinkstone at the Puys-de-Oriou 

 and adjacent places is more modern than the trachytes and basalts ; 

 and that its eruption forced up these rocks, breaking the whole 

 volcanic group of the Cautal into those radiating valleys we now see, 

 and which diverge from the central part of the group outwards. 



The Honts-Dor constitute another somewhat circular syst< 

 volcanic mountains, about four leagues in diameter, and rising at the 

 Puys-de-Sancy to the height of 0190 feet above the sea the most 

 elevated point of Central France. The trachytic rocks are here also 

 the most ancient volcanic products, and occupy the central and 

 largest part of this group of mountains, the basalts skirting the 

 general mass, though they are not strictly confined to the outer 

 portions, patches of basalt occurring among the trachyte of the 

 ulterior. The whole rests on the granite and other ancient crystalline 

 rocks of Auvergne. Trachytic conglomerates alternate with <>liil 

 trachyte, and the latter is often divided into prism* as beautiful as 

 those of basalt The upper bed of trachyte is the thickest, and 

 forms the rock beneath the greater part of the pasture* of Monte-Dor. 

 Veins of trachyte are well seen in the Vallce-den-Enfers. Mora 

 modern volcanic action can be traced around the great central mass 

 of these mountains at Monteynard and the Puys-d'Enfer ; and scoria) 

 extremely fresh are observable at the Puys-Vivanson and the Puys- 

 d'Aiguillicr. 



The great proportion of the more modern volcanoes of Auvergne 

 occur in the vicinity of, or at moderate distances from, the town ..f 

 Clermont It would far exceed our limits to enter into a detail of 

 the volcanoes which are found in this part of Auvergne, and which 

 possess various degrees of interest according to the situations where 

 they occur, and the rocks with which they are associated. Though 

 they are for the most part distinguished by craters in different states 



