364 Analysis of Scientiflc Books and Memoirs. 



Sioule by a narrow gully twelve feet tleep and ten wide, perforated in the 

 mica schist. Before this passage had been effected, the basin must have 

 been a lake, the sediments of which consist of a black desiccated bitumi- 

 nous clay disposed in thin flakes. Iron pyrites is extremely abundant in 

 this clay, and in many points the pyrites seems to have undergone a 

 spontaneous combustion, and the clay of the strata round been in conse- 

 quence converted into tripoli, of which the parts most exposed to the 

 heat are of a bright red, the others varying between pink, yellow, and white. 

 These baked beds occasionally alternate eight or ten times with those that 

 are untouched. The tripoli, which is very light, separates with facility in- 

 to the finest folia ; but it is so brittle that it must be taken out with 

 great care by the hand. It is then dried in the sun, and needs no farther 

 preparation for the market. Besides the casts of fish, Mr Scrope observed 

 casts of numerous leaves between the laminae, which were perfect and 

 beautiful. They resembled those of the willow, the elder, and the syca- 

 more. The fish were very imperfect, but bore some resemblance to the 

 carp and the eel. 



Previous to giving an account of the volcanic formations of central 

 France, JMr Scrof)e has favoured us with some interesting notices of the 

 labours of those geologists who have written on the volcanic remains of 

 that district. When MM. Guettard and Malesherbes passed through 

 Montelimart in 1751 on their return from Italy, where they had visited 

 Vesuvius, they observed the street pavement formed of short articulations 

 of basaltic columns fixed vertically in the ground, and learning that they 

 were from the rock of Rochemaure, and were found also in the Vivarais, 

 they visited that province, and made known its volcanic character. (See 

 Mem. Acad. For. 1752.) The views of these naturalists obtained at first 

 little credit, but M. Desmarest afterwards removed every doubt by his Me- 

 moirs on the Origin oj Basalt, which appeared in those of the academy for 

 1771. In 1778, Faujas de St Fond published his work entitled '' Bes Vol- 

 cans eteints du Vivarais ct Velay ;" but he unluckily found a crater in every 

 chasm and decomposed lavas in beds of marl and sandstone. It was now, 

 however, universally admitted that numerous volcanos had broken out in the 

 interior of France, at different and very remote periods, and had covered 

 with the products of their eruptions the provinces of Auvergne, Velay, and 

 Vivarais. M. Dolomieu glanced at this district in 1797, and in 1802 M. 

 de Montlosier published his work sur la Theorie des Volcans d' Auvergne, 

 and exhibited the various relations and characters of those volcanic remains; 

 M. de Buch, IM. Lacoste, Baron Ramond, and Dr Daubeny, have more re- 

 cently employed their talents on the same subject. 



Mr Scrope next proceeds to give a general account of the two classes of 

 volcanic formation in Auvergne, and afterwards a detailed description of the 

 four regions into which he divides the volcanic district, viz. 1. Mont Dome 

 of the Limagne of Auvergne. 2. The Mont Dor. 3. Cantal, and 4. The 

 Departments of the Haute Loire and Ardeche. In his account of the first 

 of these regions we meet with the following interesting observations on 

 the nature and origin of trachyte. 



