COAL MINES OF EASTERN VIRGINIA. 535 



of this mine was found to be 61,° 5 ; but in this case it was evi- 

 dent that a large amount of liquid flowed from the upper strata 

 and thus reduced the temperature of the whole. 



4. Wills and MichaeVs Pit. The works were in active pro- 

 gress in this mine when the observations were made. The tem- 

 perature first noted was that of the water at the bottom of the 

 main shaft ; the second, that of a similar pool in the lowest level. 

 The results were — 



Depth. Temperature. 



386 feet, 62." 



570 " 65.5 



11. Observations made in Shafts either just completed or 



IN progress. 



1. Black Heth New Shaft (1836). This shaft, which was in 

 progress at the time of my observation, had reached the depth of 

 380 feet. The water at the bottom, which collected rapidly, was 

 derived in part from the small streams flowing in from the adja- 

 cent rock, and partly from that which dripped from the edges of 

 the higher strata. The temperature of the liquid in a small pool 

 was 60". That of the rock, as shown by a thermometer inserted 

 deeply into a crevice on one side, was 61." 5. But the free access 

 of moisture and air had no doubt depressed the temperature 

 slightly, even in this position. Upon exposing the bulb to a 

 stream of drops coming from some distance above, it indicated a 

 temperature of 59°. It is therefore evident that the true tempera- 

 ture of the rock, at the bottom of this shaft, is somewhat over 

 61.° 5. 



Depth. Temperature. 



380 feet, . ■ 61. °5 



2. Mid Lothian New Shaft (1839). This shaft, cutting 

 through a seam of coal 36 feet thick, penetrated a coarse grit 

 for a few feet, and then struck into the sienitic floor. Imme- 

 diately above and beneath the coal, and from the rock in contact 



