1870.] 



Mr. E. Hull on the Temperature of Strata. 



175 



mean temperature of the place. With these data, the increase is 1° F. for 

 every 54*57 feet, which approximates to that obtained by Professor Phil- 

 lips at Monkwearmouth of 1° F. for ahout every CO feet. 



If, on the other hand, for the purpose of comparison, we adopt the mea- 

 surements for the invariable stratum as obtained at Dukenfield, we find 

 the rate of increase to be 1° F. for every 47'2 feet as against l°F. for every 

 83*2 feet in the case of Dukenfield itself. So great a discordance in the 

 results is remarkable, and is not, in my opinion, attributable to inaccuracy 

 of observation in making the experiments. On the other hand, I may ven- 

 ture to suggest that it is due, at least in some measure, to dissimilarity in 

 the position and inclination of the strata in each case. These I now pro- 

 ceed to point out. 



Position of the Strata at Rose Bridge and Dukenfield Collieries. — 

 Rose Bridge Colliery occupies a position in the centre of a gently sloping 

 trough, where the beds are nearly horizontal ; they are terminated both on 

 the west and east by large parallel faults which throw up the strata on 

 either side. The colliery is placed in what is known as " the deep belt." 



Dukenfield Colliery, on the other hand, is planted upon strata which 

 are highly inclined. The beds of sandstone, shale, and coal rise and crop 

 out to the eastward at angles varying from 30° to 35°. Now I think we 

 may assume that strata consisting of sandstones, shales, clays, and coal 

 alternating with each other are capable of conducting heat more rapidly 

 along the planes of bedding than across them, different kinds of rock 

 having, as Mr. Hopkins's experiments show, different couducting-powers. 

 If this be so, we have an evident reason for the dissimilar results in the 

 two cases before us. Assuming a constant supply of heat from the interior 

 of the earth, it could only escape, in the case of Rose Bridge, across the 

 planes of bedding, meeting in its progress upwards the resistance offered 

 by strata of, in each case, varying conducting-powers. On the other hand, 

 in the case of Dukenfield the internal heat could travel along the steeply 

 inclined strata themselves, and ultimately escape along the outcrop of 

 the beds. 



I merely offer this as a suggestion explanatory of the results before us, 

 and may be allowed to add that the strata at Monkwearmouth Colliery, 

 the thermometrical observations at which correspond so closely with 

 those obtained at Rose Bridge, are also in a position not much removed 

 from the horizontal, which is some evidence in corroboration of the views 

 here offered. 



