beneath the surface of the Earth. 17 



the city of Tours in the basin of the Loire.* The spring ceasing 

 to flow so freely, it became necessary to draw out the tube to within 

 twelve feet of the surface. Immediately the water gushed out one 

 third more plentifully, and continued so for several hours, carrying 

 with it a large quantity of fine sand, and many remains of plants and 

 shells. Among these were twigs of several inches in length blacken- 

 ed by the action of the v/ater ; fresh stems and roots of marsh plants, 

 — of one species in particular so fresh, that they could not have lain 

 more than three or four months in the water ; seeds of five or six dif- 

 ferent species; and fresh water and land shells, {JPlanorhis margi- 

 natus. Helix rotundata and striata.) All these are such remains as 

 are found after a flood on the banks of small streams. 



The water in this remarkable case, therefore, must proceed from 

 some subterranean stream, the source of which is to be sought for at 

 a distance among the higher grounds of Auvergne and Vivarais, and 

 from the temperature of such sources, it is evident we can infer 

 nothing regarding the interor temperature of the earth. 



M. Magnusf has made some observations on the temperature of a 

 boring at Rudensdorf, about five German miles from Berlin, which 

 seem entitled to some confidence. It passes through limestone, gyp- 

 sum, and sandstone, alternating with clay-slate, to a depth of sixty five 

 English feet. The mean temperature of the place on which no ex- 

 periments have been made is assumed to differ very little from that of 

 Berlin, 49.1° F., and the results are as follows : 



Temper. Diff. from mean. For 1° F. 



At 675 feet 67.66 +18.56 36.3 feet. 



516 63.95 +14.85 34.7 



393 62.82 13.72 28.5 



The first of these results is the only one to which we can look for 

 any approximation to the truth. And it comes very near 36.81, the 

 result of Kupffer. The other determinations, however, are not with- 

 out their value, they all indicate a more rapid increase of temperature 

 than the truth, as we should naturally expect. For though the water 

 as it gushes from the bottom of the tube must undergo considerable 

 cooling on its way to the surface, yet it must still retain a considerable 

 excess over the temperature of the strata through which it passes, and 

 thus indicate a less distance for each degree of the thermometer, as 



* Pogs- Ann. xxi. p. 353. I Pog. Ann. xxii. p. 146. 



Vol. XXIII.— No. 1. 3 



