TERRESTRIAL PHENOMENA. 149 



not extend beyond a vertical depth of somewhat more than 

 2000 feet (about one-third of a geographical mile) below the 

 level of the sea, and consequently only about g--Vo of the 

 Earth's radius. The crystalline masses that have been erupted 

 from active volcanoes, and are generally similar to the rocks 

 on the upper surface, have come from depths, which although 

 not accurately determined, must certainly be sixty times 



exactly 1993 feet, the absolute depth being 2231 feet. The temperature 

 of the water at the bottom was 91F., which, assuming the mean tempera- 

 ture of the air at 49'3, gives an augmentation of temperature of 1 for 

 every 54 feet. The absolute depth of the artesian well of Grenelle, near 

 Paris, is only 1795 feet. According to the account of the missionary 

 Imbert, the fire springs, " Ho-tsing," of the Chinese, which are sunk to 

 obtain [carburetted] hydrogen gas for salt-boiling, far exceed our artesian 

 springs in depth. In the Chinese province of Szll-tschuan these fire 

 springs are very commonly of the depth of more than 2000 feet ; indeed, 

 at Tseu-lieu-tsing (the place of continual flow) there is a Ho-tsing which, 

 in the year 1812, was found to be 3197 feet deep. (Humboldt, Asie 

 Centrale, t. ii. pp. 521 and 525. Annales de I' Association de la Propa- 

 gation de laFoi, 1829, No. 16, p. 369.) 



The relative depth reached at Mount Massi, in Tuscany, south of Vol- 

 terra, amounts, according to Matteuci, to only 1253 feet. The boring at 

 the new salt works near Minden, is probably of about the same relative 

 depth as the coal-mine at Apendale, near Newcastle-uuder-Lyme, in Staf- 

 fordshire, where men work 725 yards below the surface of the earth. 

 (Thomas Smith, Miner's Guide, 1836, p. 160.) Unfortunately, I do not 

 know the exact height of its mouth above the level of the sea. The relative 

 depth of the Monk-wearmouth mine, near Newcastle, is only 1496 feet. 

 (Phillips, in the PMlos. Mag., vol. v., 1834, p. 446.) That of the Liege 

 coal-mine, VEsptrance, at Seraing, is 1355 feet, according to M. von 

 Dechen, the director; and the old mine of Marihaye, near Val-St. -Lam- 

 bert, in the valley of the Maes, is, according to M. Gernaert, Ingenieur des 

 Mines, 1233 feet in depth. The works of greatest absolute depth that 

 have ever been formed are for the most part situated in such elevated 

 plains or valleys that they either do not descend so low as the level of the 

 sea, or at most reach very little below it. Thus the Eselschacht, at Kut- 

 tenberg in Bohemia, a mine which cannot now be worked, had the enormous 

 absolute depth of 3778 feet. (Fr. A. Schmidt, Berggesetze der Vster Mon., 

 abth. i. bd. i. s. xxxii.) Also, at St. Daniel and at Geish, on the Rorer- 

 biihel, in the Landgericht (or provincial district) of Kitzbiihl, there were, 

 in the sixteenth century, excavations of 3107 feet. The plans of the works 

 of the Rb'rerbuhel are still preserved. (See Joseph von Sperges, Tyroler 

 BergwerJcsgeschichte, s. 121. Compare also Humboldt, Gutachten uber 

 Herantreibung des Meissner Stollens in die Freiberger Erzrevier, printed 

 in Herder, uber den jetz begonnenen Erbstollen, 1838, s. cxxiv.) We 

 may presume that the knowledge of the extraordinary depth of the Rorer- 



