the Prussian Coal-Mines. 189 



niting basalt from Unkel, and other localities, in a glass fur- 

 nace, in order to ascertain if any carbonic acid would be 

 evolved, I noticed the evolution of an inflammable gas." At 

 that time I w^as much surprised by the occurrence ; but now^ it 

 no longer appears strange, when regarded as a consequence of 

 the presence of bitumen. It is likewise easily understood, 

 that, when those strata nearest the earth's surface, which have 

 been broken through by Plutonic masses, are poor in organic 

 remains, the bitumen of these masses may have been derived 

 from coal strata lying at a greater depth. It would, therefore, 

 not be ver}^ remarkable were we to find bitumen in the gra- 

 nite which had burst through the chalk. 



In your " Basalt Gebilde" (Part 2d, p. 471), you state, as a 

 fact connected with the physical history of the baths of Boll,t 

 that, during the burning that took place there between 1633 

 and 1674:, minei*al-oil flowed in such quantity from the slate, 

 that it was collected and sold. It is very likely that evolu- 

 tions of inflammable gas occurred at the same time. No em- 

 pyreumatic oil makes its appearance in what is, called the 

 burning mountain of Duttweiler, The fumaroles from the 

 fissures of the clay-slate have no burning smell, and no smoke 

 is to be observed ascending from them. This circumstance, 

 when I fii'st visited the locality about a year and a half ago, 

 excited doubts in my mind as to whether there really was a 

 coal-bed still in a state of ignition. At my request, Mr Sollo, 

 mining counsellor, and director of the mining establishment 

 at Saarbruck, had the goodness to cause a bore to be made 

 in the direction of the bed, and to a depth of 47 feet. At 

 my second visit to the burning mountain, dm'ing the last 

 autumn, I made observations on the temperature of the bore. 

 Directly under the earth's surface, I found a temperatm-e of 

 54^ R. (153^50 F.), and at a depth of five feet 69° R. (187°.25 

 F.) ; and this temperature remained the same at the deepest 

 part of the bore. I left a copper vessel filled with oil for a 



* See my " Wdrmdehre," p. 316. 



t A watering-plaro in W iirtemboi-g, situntcd at the base of the Vunihe 

 Alp. — Edit. 



