BASALT. 



Siiex 



Alumine 

 Lime 

 Magneiia 

 Soda 



Oxyd of iron 

 Oxyd of manganefe 

 Muriatic acid - 

 Water and volatile 1 

 matter - ) 



Bifa!t of the Haflenbcrg. 

 44.50 

 16.75 



9.50 



2.25 



2.60 

 20.0 



Bafalt of Stafli. 



48.0 



16.0 



9.0 



4.0 

 16.0 



I.O 



Klaproth 97.72 Kennedy 98 



Bafalt exifts abundantly in the northern parts of England 

 and in Scotland. It occurs at the Clee Hills in Shropftiire, 

 and at Rowley in StafFordfhire ; but is not met with in the 

 fouthem counties of England. Some rocks of the trap or 

 bafaltic formation occur in Gloucefterfhire and Somerfet- 

 fliire. Bafalt forms the well-known columnar ranges at the 

 Giant's Caufeway in the county of Antrim, and at Staffa. 

 See Giant's Caufeway and Staffa. 



The origin of bafaltic rocks has excited much attention 

 among geologifts. Their fimilarity to volcanic rocks in 

 compofition and ftrufture, the remarkable pofitions in which 

 they occur, and the changes they frequently produce on the 

 rocks in their vicinity, have led moft intelligent and unpre- 

 judiced obfervers to the concluCon, that a great number, if 

 not all, bafaltic rocks have been formed by igneous fufion. 

 The mineral veins fiUed with bafalt, that interfeft other 

 rocks, frequently produce all the changes which a fluid mafs 

 of heated lava would have effefted. ( See Veins, Mineral, 

 and Tkap.) In the latter article, the arguments which 

 have been offered againft the igneous origin of bafalt are alfo 

 dated. For further remarks on the fubjeft, fee Syfiems of 

 Geology. But the moft ftriking phenomena, and which 

 feem to decide the queftion, are prefented in the diftrifts 

 called Velay and Viverais, in the fouth of France. Thefe 

 diftrifts have all the appearance of ha\-ing been once the feats 

 of aclive volcanoes, the remains of which are diftinftly 

 vifible : from fome of thefe ancient volcanoes, the lava may 

 be traced to the crater, and this lava is a compaft columnar 

 bafalt. See Phite II. Mineralogy, Bafalt. 



The mountain of Aifa, called La Coupe, or the Col d'Aifa, 

 of which a view is given, is fituated near the village En- 

 trague, in the Viverais. This village, according to St. Fond, 

 is placed on a kind of platform of volcanic matter above the 

 torrent of the Volant, which has here excavated a bed of great 

 depth and width, bordered on the right and left by grand 

 ranges of bafaltic columns. In the midft of a prodigious 

 rampart of thefe columns, at different levels, may be feen a 

 current of lava defcending from a neighbouring mountain, 

 and joining the columns that border the river. Here we fee, 

 in the moft unequivocal and convincing manner, that the 

 lava under the form of hard and compaA bafalt, has flowed 

 at feveral times from the mountain, and has formed the great 

 caufeway at different heights, to which the lava is ftill 

 united and adhering. We may follow the current of bafalt 

 up the decUvity of the mountain, which has a conical form 

 and a great elevation, and is entirely volcanic from the bafe 

 to the fummit. According to St. Fond, it is the moft 

 remarkable and beft charafterifed crater in all the Viverais. 



All the bafe of the conical mountain La Coupe is covered 

 by porous and cellular lava in detached irregular maffes, 

 heaped on each other, fo as to leave no doubt that they have 

 been ejefted in a liquid ftate by one or more formidable 



eruptions, and have taken their forms as they fell at the foot 

 of the cone. 



On reaching the fummit or edge of the crater we 

 may fee the whole mountain, which forms a regular cone 

 refembling that of Vefuvius. The edges of the crater are 

 fteep, and formed in the fhape of a tunnel ; the greateft dia- 

 meter being from 1 40 to 150 toifes, and the depth about 600 

 feet. The lavas are coloured, and converted into a kind of 

 puzzolani, and mjxed with great maffes of black and fharp 

 fcona, which makes the defcent difficult. At the bottom of 

 this inverted cone is a magnificent plantation of chefnut-trecs, 

 which have flourifhed aftonifliingly in this ancient mouth of a 

 volcano, having no other foil than the dry and friable puz- 

 zolani. It may be noticed, that the crater of Vefuvius was 

 hned with lofty trees at the period of its eruption in 1631, 

 having been in a ftate of repofe for nearly four hundred 

 years. 



At the bottom of the crater in La Coupe, we may ob- 

 ferve a breach or opening on the fide facing the houfes of 

 the Colet d'Aifa ; there is a general inclination to this open- 

 ing, which has ferved to give a paffage to the lava. When 

 we are arrived at the opening, we may obferve a ftream of 

 lava coming from the interior, and taking its courfe down 

 the mountain, it defcends in a waving direftion amidft tlie 

 porous lavas. This current is a true black bafalt, compaft 

 and fimilar to that of the columns ; in certain parts, its fur- 

 face appears bliftered, and in other places is become porous. 

 Following the current of lava, after it has crofTed the path, 

 which is at the foot of the mountain, we may trace its 

 courfe to the bed of a torrent not far from the high road. 

 There may be feen, fays St. Fond, a fpeftacle moft gra- 

 tifying to the geologift ; for the lava, whilft ftill on the 

 defcent, and before it had reached the level ground, has 

 affefted a prifmatic form ; and the lava at the bottom has 

 formed a beautiful colonnade. 



We cannot doubt, fays St. Fond, after vievring this 

 mountain, that the lava which flows from volcanic craters 

 is not abfolutely the fame as bafalt. The name of La Coupe 

 is evidently derived from the crater, the Latin name ft>r 

 a cup. 



There is another conical mountain in the Viverais with 

 a diftinft crater, called La Coupe de Jaujeac. The ge- 

 neral refemblance of the latter is fo fimilar to that of La 

 Colet d'Aifa, that it may well be conceived from the view 

 given of the latter. (See Plate 11. Mineralogy.) It is 

 rather lefs lofty, but the crater is nearly twice as large. 

 The river Vignon flows at the foot of Jaujeac. On its 

 banks are immenfe ranges of bafaltic columns, the moft ele- 

 vated of any in the Viverais. They inclofe the borders of 

 the river on each fide for more than a league. 



Some of the prifms rife in one fhaft to the height of fifty 

 feet ; in other parts, the articulated columns form a kind of 

 regular caufeway. In fome places the columns are bent, 

 and above we fee immenfe ramparts of bafalt, of more than 

 140 feet in height, in feveral ranges, fpreading out like a 

 fan, and diverging in every direftion. On the left, the current 

 of bafalt covers feveral little hills of granite, and is moulded 

 upon them. In fome parts, the compaft lava forms one fohd 

 mafs ; in other places, it is arranged in great beds. Nothing 

 can be more grand and varied, fays St. Fond, than the 

 courfe of the river Vignon to Ardeche, where the great 

 current of lava joins the ftrearas that have flowed from the 

 volcanoes of Theuyts and Neyrac. Faujas St. Fond fur les 

 Volcans eteints du Viverais et du Velay. 



PJaie II. Mineralogy, Bafalt, vrhich is taken for this work, 



will convey at once a farisfaftory proof of the igneous origin 



of the bafaltic columns in the Viverais ; but one engraver 



3 B 2 has 



