On Underground Temperatures. 25 



possibly have acquired the temperature of the circumjacent body of 

 strata ; or the place might be bricked up.* 



It is only in a few instances that temperature observations have 

 been made in carboniferous strata in other than coal-pits; in 

 these others there is no indication of the excessive range which the 

 observations in shafts and galleries have shown. The following 

 table gives the results obtained in bore-holes sunk in search of coal. 

 At Creuzot there is a thick capping of Triassic strata, and the coal 

 strata dip rapidly. 



Original 

 number. 



Place. 



Depth. 



Eate of 

 increase for 

 1° F. 



123 

 124 

 68 

 69 





feet. 

 347 

 525 

 1817 

 2677 



feet. 

 52 

 42 

 57 

 52 



Mean 50 '8 



If we were to unite these two series of observations, we should get 

 for the Coal-measures a rate of increase of temperature as nearly as 

 possible of 50 feet per degree Fahr., although there seems to be local 

 variations dependent upon structure, the percolation of water, and 

 other causes. 



II. Mines other than Coal. (Table III, p. 96.) 



The causes affecting the thermal conditions of Metalliferous Mines 

 are very different to those which obtain in Coal Mines. In them 

 we have to deal almost exclusively with crystalline and schistose 

 rocks. Not only does the conductivity of such rocks differ materially 

 from that of the Coal-measures, but the disturbing causes common to 

 the two have in general very different values. 



Ventilation is a cause affecting both, but it affects them unequally ; 

 and while in Coal Mines the influence of water is generally very small, 

 it plays an important part in Metallic Mines. On the other hand, 

 chemical decomposition and hot springs, which are common disturbing 

 causes in the latter, are of rare occurrence in the former. 



Ventilation. — I have so fully described the effects of ventilation in 

 the section on Coal Mines, that I only need mention here in what 

 respects its effects differ in other mines. Besides, we are not in pos- 

 session, in respect to metallic mines, of such detailed particulars as 

 those which the Report of the Coal Commission gives of the Coal 



* Or, deeper holes and well distant from the shaft might answer. 



