1814.] An Account of the Basalts of Saxony. 147 



at the time of its deposition, had been in a state of fusion from 

 heat. Basalt sometimes alternates with limestone ; and Dolomieu 

 describes no fewer than 20 beds of basalt alternating with as many 

 beds of limestone containing marine shells. All these, and many 

 other examples quoted by Dauhuisson, are inconsistent with the 

 notion that basalt is lava. The same incompatibility follows from 

 the feet that the rock immediately under the basalt, whether clay, 

 sand, mica slate, gneiss, granite, or porphyry, is not the least 

 altered in its texture, as would undoubtedly have been the case had 

 the basalt been deposited on it in a state of fusion fiom heat. 



M. Daubuisson concludes his essay with a general review of the 

 whole, in which he seems rather to incline to the opinion that 

 basalt is always of aqueous origin, and never produced by heat. He 

 finally gives a more detailed account of the properties of basalt than 

 he had given at the commencement of his essay. 



Of the notes that accompany this essay, the only one of which it 

 seems requisite to give an account is that in which the result of 

 Daubuisson's examination of Auvergne is given, because it informs 

 us that he has found it necessary to modify somewhat his former 

 opinions on this subject. He was advised by the French Institute, 

 some of whom are zealous volcanisls, to make this tour, and he 

 performed it in 1804. The base of Auvergne he found to be 

 granite. In the western part it is covered by gneiss and mica slate, 

 containing metallic veins, and in some places with greenstone slate. 

 In the valley of the Allien, limestone appears containing silicious 

 concretions, and much impregnated with bitumen. In the low 

 district, where the Alagnon falls into the Allier, a coal country 

 occurs. Every where else the granite serves as the immediate 

 support of the volcanic hills. The chain of Puys extends for above 

 20 miles. Most of them stand detached. Their form is generally 

 that of a truncated cone; their sides are inclined at an angle of 

 about 30°, and on their summits there is generally a cup-like de- 

 pression, which is sometimes 200 feet deep. Their general eleva- 

 tion is from 900 to 1300 feet above the plain ; the central and 

 highest, the Puy de Dome, being near 2000 feet. 



The substances which chiefly compose these hills are described 

 under the titles of Spongy Scoria 1 , which are often of a bright red 

 colour; twisted, or rope-like scoriaa (tcories cordees) ; lapillo, or 

 volcanic gravel; vesicular, or blistered lavas (laves boursnuffli-es) ; 

 and basaltic lava (lave basakique). In most cases these substances 

 are confusedly heaped together ; but the Puy de Dome, and two or 

 three others, form exceptions. 



The sides of most of the Puys are covered with herbage and 

 brushwood ; a few are wooded. On the top, as already mentioned, 

 i^ (generally found a crater, which is sometimes broken down on the 

 side from which the lava had flowed. One of the most perfect 

 examples is the Puy de Pariou ; and Mr. Daubuisson's description of 

 this is j-iven at full length in the Journal de Physique. Its crater is so 

 entire, and to nicely formed, that it appears as if •« turned on a loom ;" 



K. 9 



