ON THE BATE OF INCREASE OF UNDERGROUND TEMPERATURE. 



27 



became distorted, so that after extracting the dry rag and clay, an hour 

 was expended in working out the thermometer, the reading of which has 

 therefore been rejected. The following is a list of the five remaining 

 stations, arranged in order of depth : — 



No. of 

 Station 



IV. 



V. 



VI. 



ni. 

 I. 



Depth 



from Surface 



in feet 



465 



555 



636 



660 

 1041 



Temperature 

 Fahr. 



53-4° 

 52-9° 

 58-8° 

 540° 

 60-8° 



Distance and 

 Direction from 



Mostyn Shaft 

 190 yds. S.W. 

 170 yds. S.E. 

 840 yds. S.W. 

 120 yds. S. 

 190 yds. N.E. 



It will be observed that the order of the temperatures is not the same 

 as the order of the depths ; it therefore becomes important to describe the 

 positions with some particularity. 



Stations IV., V., and III. are near together in ground plan, IV. and V. 

 being about 250 yards apart, and III. nearly midway between them, and 

 they have all the same rock overhead between them and the surface, 

 namely, black and white limestone. 



At Station I. the rock overhead consists almost entirely of sandstones 

 and shales, with thin coal-seams. At Station VI. it consists of white 

 limestone and shale. 



It may be mentioned that the temperature at VI. was observed on three 

 several occasions, namely, January 14, January 21, and February 19, and 

 was in each case found to be the same. Mr. Strahan further states that 

 this station is near a large fault, which contains iron pyrites and gives off 

 water charged with sulphuretted hydrogen ; the temperature of the water 

 as pumped up "Walker's shaft from a depth of 770 feet, being 63° at the 

 top of the lift. It seems probable that the decomposition of this pyrites 

 may be the cause of the exceptionally high temperature at this station. 



The comparison of the temperatures will be most clearly brought out 

 by tabulating the rate of increase from the surface down to each station, as 

 calculated from an assumed surface temperature, which may be fairly 

 taken as 48°. As all the depths are considerable, an error of a degree in 

 the surface temperature will not have much influence on the comparison, 

 which stands thus : — 



Station 



IV. 



V. 



VI. 



in. 

 I. 



Stations V. and III., which give the slowest rate of increase, are both 

 of them in a vein called the ' South Joint ; ' and Stations IV. and I., which 

 agree well with each other, though differing from the rest, are both of 

 them in another vein called the ' Talargoch vein ; ' while Station VI. 

 is in the rock. The horizontal distance between IV. and III. is only 

 120 yards : but if we attempt to deduce the rate of increase from com- 

 paring these two, we have an increase of only 0'6° in 195 feet. It thus 

 appears that, notwithstanding the proximity of the two veins, their con- 

 ditions as to temperature are very different. 



Widely as the results differ among themselves, they agree upon the 

 whole in showing that the average rate of increase is slow; and this 



