20 



Prof. J. Prestwich. 



the circumstance that at this point the surface of the ground has 

 risen so much that the seam of coal lies 1690 feet below the surface, 

 or 1330 feet lower than at the bottom of the shaft. The distance 

 from the shaft might partly account for this difference, but only 

 partly for that between stations 2, 3, and 4. 



At the Cym Neol Colliery one station is under a valley, and two 

 under the adjacent hills, rising about 500 feet above the valley. No. 2 

 station is only 480 yards distant from shaft (not in section), against 

 1070 from Station No. 1, and 1350 yards from Station No. 3. At 

 that time the temperature of the outer air was 69° P. 



Fig-. 2. — Section at Cym Neol, Aberdare District. 



In a similar way the New Tredegar Colliery is situated in a valley 

 670 feet above the sea level, and the works pass under a hill which 

 rises 617 feet above the valley, with the effect of raising the tempera- 

 ture of the same coal 11° P., though 2° to 3° of this may be owing to 

 distance from shaft. At the time the thermometer outside stood at 

 60° to 70° F. 



Fig. 3. — Section at New Tredegar, Aberdare District. 



At the Vochriw Dowlais Colliery, on the other hand, the top of the 

 shaft is on a hill 1330 feet above the sea level, and the seam of coal, 

 which there lies 1103 feet below the surface, is followed first under a 

 hill which rises 217 feet above the pit mouth, and then under a valley 

 only 818 feet above sea level, or 512 feet lower than the pit mouth. 

 Notwithstanding the distance of Station No. 3 from the shaft, the fall 



