1870.] Observations on Underground Temperature. 211 



same coal-seam being thereby placed at a less depth from the surface 

 than in the case of the " deep belt." 



Between these faults the strata incline at small angles, generally- 

 dipping gently to the eastward. 



Nearly in the centre of one of these " deep belts," Eose Bridge 

 Colliery is situated; the belt being bounded on the west by the 

 " Standish fault," along which the strata are let down on the eastern 

 side about 150 yards; and on the east, by the Kirkless Hall fault, 

 along which the strata are let down on the west about 600 yards. 

 At the colliery itself the strata are almost horizontal ; consequently 

 all the strata, except those comparatively shallow, are broken off by 

 the large faults above described before they reach the surface. 



Dukinfield Colliery. — The circumstances of the strata at this 

 colliery are very different from those of Eose Bridge. The pits are 

 situated on the Cheshire side of the river Tame, near Ashton- 

 under-Lyne, and in this district the beds rise and crop out to the 

 eastward at high angles. At the colliery, the dip is west at about 

 35°, and the " Black Mine" (or coal), which was reached at a depth 

 of 2151 feet, crops out at a distance to the eastward of little more 

 than 1000 yards. 



From this account it will be seen that we have very different 

 stratigraphical conditions in each locality, and to this I attribute in 

 a great measure the difference in the rate of increase of underground 

 temperature in these localities respectively. For purposes of com- 

 parison we may assume a constant supply of heat from the interior 

 of the earth, tending to travel towards the surface. In its progress 

 it meets with strata of different conducting powers, the thermal 

 conductivity of each stratum in the same locality being in the inverse 

 ratio of the rate of increase, as shown by Mr. W. Hopkins, F.E.S.,* 

 in other words, where the rate of increase is rapid the conducting 

 power is small. 



But whatever may be the conducting power of a series of strata, 

 it seems probable that it is impeded when the heat has to travel in 

 a direction perpendicular to the planes of bedding. On the other 

 hand if the heat can find its way towards the surface partly along 

 the planes of bedding, the thermal conductivity is increased, and the 

 rate of increase is proportionally lessened ; for in this way it may 

 be conveyed by strata which have high conducting powers, and 

 escape along the outcrop of the strata themselves. 



If this view be correct, we can at once account for the difference 

 in the results at Eose Bridge and Dukinfield collieries. In the 

 former, owing to the horizontality of the strata, the heat can only 

 find its way outwards directly across the planes of bedding. We 

 may, therefore, suppose that the resistance to its motion is increased 

 thereby ; the conductivity is lessened, and, in consequence, the rate 



* ' Philosophical Transactions,' vol. cxlvii. 



