ON THE BATE OF INCREASE OF UNDERGBOUND TEMPEBATUBE. 83 



in the Dakinfield mines are so dry that this action does not seem to be 

 important.^ 



E. We now proceed to a comparison of results. The localities at 

 which definite results have been obtained may be thus classified : — 



1, Metallic mines. 2. Coal mines. 3. Wells and wet borings. 

 4. Tunnels. 



1. The mines at Pkzibbam in Bohemia (VII. 15), with a depth of 1,900 

 feet, are in very quartzose rock, and give a very slow rate of increase, 

 viz. 1°-1 in 136 feet. As all the shafts are in lofty hills, an allowance of 

 -jLmay be made for convexity, leaving 1° F. in 126 feet. Quartz is found 

 by Professor Herschel to have a conductivity of about '0086. 



The mines at Schemnitz in Hungary (X. 194), with a depth of 1,368 

 feet, give an average rate of 1° F. in 74 feet, the rock being a green 

 hornblende-andesite (in German, G^-ihistein-Trachjt), which is a compact, 

 igneous, more or less vitreous rock. Professor Lebour estimates its 

 conductivity as being probably nearly the same as that of Calton Hill 

 trap-rock, which Professor Herschel found to be about •0029. 



The Talakgoch lead mine (Flintshire) (XIII., XIV.), with its veins 

 running across carboniferous limestone, has a depth of 1,041 feet, and gives 

 in various parts rates varying from 1° in 47 feet to 1° in 113 feet. The 

 average may be taken as 1° in 80 feet. 



2. The results from coal mines are as follows, beginning with foreign 

 mines : — 



The mines of the Societe Cocqueril at Seraing (Belgium) (VII. 17), 

 with a depth of 1,657 feet, give an average rate of 1° F. in 60 feet. The 

 reck is coal shale. Professor Herschel found for shale the low conduc- 

 tivity of -0019. 



The mines of Anzin, in the north of France (IX. 210) with a depth of 

 658 feet, gave in the deepest shaft an increase of 1° in 47 feet. 



EosEBRiDGE CoLLiERT, near Wigan (III.), with a depth of 2,445 feet, 

 gave a mean rate of 1° in 64 feet. 



The four following are in the East Manchester coalfield : — 



Astlet Pit, Dukinfield (III., XIII.), with a depth of 2,700 feet, gave 

 1° in 72 ft. 



AsHTON Moss Colliery (XIV.), with a depth of 2,790 feet, gave 1° in 

 77 feet. 



Bredburt Colliery (XIV.), with a depth of 1,020 feet, gave 1° in 78-5 

 feet. 



Nook Pit (XIV.), with a depth of 1,050 feet, gave 1° in 79 feet. 



Denton Colliery, Lancashire (XV.), with a depth of 1,317 feet, gave 

 an increase of 1° in about 77 feet. 



South Hetton CotLiERY, Durham (V. 132, VI. 254), with a depth of 

 1,929 feet, including a borehole at bottom, gives very consistent observa- 

 tions at various depths, and an average rate of 1° in 57'5 feet. 



Boldon Colliery, between Newcastle and Sunderland (X. 197), with a 

 depth of 1,514 feet, and excellent conditions of observation, gives an 

 average rate of 1° in 49 feet. 



Whitehaven Colliery, Cumberland (XV.), in workings under the sea, 

 with a depth of 1 ,250 feet beneath sea-level, or about 1,178 feet beneath the 

 sea-bottom, gave an increase (from the sea-bottom) of about 1° in 45 feet. 



KiNGSWooD Colliery, near Bristol (XII.), with a depth of 1,769 feet, and 



• Though the workings are dry, there is a large quantity of water in the super- 

 incumbent strata. See Report XV. 



g2 



