[ 4-36 ] 



XC. All Accoimt of the Observations, and Exjyerimcnts on 

 the Temperature of Mines, which have recently been made 

 in Cornxvall, and the North of Englcmd ; comprising the 

 Substance of various Papers on the Subject lately published 

 in the Transactions of the Royal Geological Society of Corn- 

 ivall, and other Works. 



[Continued from p. 353.] 



III. T^R. FORBES's paper (Transactions of the Geological 

 ■*-^ Society of Cornwall, vol. ii. p. 1 59) consists of two 

 parts, in the first of which he gives the original registers of his 

 observations on the tempei'atures of various mines in Corn- 

 ■wall; discussing, in the second, the effects of extraneous 

 sources of heat in contributing to the elevation of their tem- 

 peratui'e; and, conceivhig that his observations irrefragably 

 prove the progressive increase of heat in the earth, as we ad- 

 vance downwards, he concludes with some remarks on the 

 probable origin of this mternal heat. 



" Before proceeding to read my registers," Di\ F. says, 

 " it may be proper, with a view to their better comprehension, 

 to premise a few brief remarks on the nature and interior 

 ceconomy of the mines in which the observations were made." 



" 1. Perhaps the clearest idea we can convey to others of 

 the nature of a metalliferous vein, or lode, is afforded by the old 

 theoretical notion, of a narrow rent in the rocky crust of the 

 earth, approaching more or less to a vertical direction, and 

 filled with metallic ores. The object of mining is to break 

 down, and transport to the surface, the contents of this sup- 

 posed rent, — in other words, to cut out from the containing 

 rock, this thin metallic plane. To effect this, galleries, called 

 in Cornwall levels, are driven horizontally on the vein, one 

 above the other, and the ore &c. produced by their excava- 

 tion are transported to the sui'face by vertical galleries called 

 shafts, cutting the former at right angles. The horizontal 

 galleries are, in the first instance, about two feet wide and six 

 feet high, but varying, of course, according to circumstances, 

 and being frequently extended much beyond their original 

 dimensions. They are driven one above the other at intervals 

 of from 10, to 20 or 30 fiithoms. When extended to a cer- 

 tain distance from the original shaft, it is necessary, for the 

 sake of ventilation, as well as for other reasons, to form a se- 

 cond, which traverses all the galleries in the same manner 

 as the first. The distance between shafts is very various, — 

 being from 20 to 100 fathoms. Frequently a communication 

 is made between two galleries by a partial shaft (called a ivins) 



in 



