23 G ANNUAL OF SCIENTIFIC DISCOVERY. 



during the sinking of mining shafts, points to the conchision of a 

 remarkable uniformity in the increase of temperature as we pene- 

 trate the earth's crust. 



Tlie surface of the basin of the artesian well of Grenelle, near 

 Paris, is 119 feet above the level of the sea, and the borings ex- 

 tend to the depth of 1,794.6 feet from the surface ; the water from 

 the lower greensand formation is at 81.95° F., an increase of 1° 

 for every 59 feet. The boring at New Saltzwerk, in Westphalia, 

 231 feet above the level of the sea, penetrates to a depth of 2,281 

 feet from the surfjice, or 2,050 below the level of the sea, — proba- 

 bly the greatest relative depth ever reached ; the temperature of the 

 brine is 91.04° F., and, as the mean annual temperature there is 

 about 49.3°, we may assume an increase of 1° F. for every 54.68 

 feet. This boring is 487 feet deeper than that of Grenelle, and 

 the temperature of the water is 9.09° higher. Other artesian 

 wells give an increase of 1° for 55 and for 57 feet. 



A great source of error in the case of mines is the heat from 

 the spontaneous combustion of pyrites. In a colliery near Sun- 

 derland, Prof. Phillips found an increase of temperature of 1° for 

 every 60 feet, at a depth of 1,590 feet, and 1,449 below the sea 

 levef ; at the Rose Bridge Colliery, near Wigan, taking the inva- 

 riable temperature at 50° at a depth of 50 feet, the increase was 

 found to be 1° for every 58.3 feet. 



The most elaborate and extensive are the observations of Mv. 

 W. Fairbairn, at the Astley pit of the Dukenfield colliery in Chesh- 

 ire, embracing a period of 10 years (1848-59), and a depth of 

 2,151 feet from the surface. From 52 recorded observations, with 

 an invariable temperature of 51° at a depth of 16^ feet from the 

 surface, the temperature at the bottom of the pit was 75.5° ; an 

 increase of 24.5° in 2,040 feet, or 1° for every 83.2 feet; the rate 

 of increase was nearly as great at the lowest depths as at any 

 portion of the descent. 



The observations of Humboldt prove that the increase of tem- 

 perature is independent of altitude of the place, or of the density 

 of the air. 



The temperature of the "invariable stratum" of Humboldt ap- 

 proximates to that of the mean annual temperature of the place, 

 and its depth is regulated, according to him, by the latitude (in- 

 creasing from the equator to the poles), by the conducting power 

 of the rock or soil, and by the amount of difference between the 

 temperatures of the hottest and the coldest seasons. At Green- 

 wich, the mean temperature is 49.5°, and that of the invariable 

 stratum about 50.5° at a depth of about 50 feet from the surface. 

 For ordinary purposes 50° F. may be taken, at a depth of 50 feet, 

 as that of the invariable stratum for the greater part of central 

 England. In France, a depth of 86 feet and 53.3° are taken. 



FOSSIL TREES. 



There exists in the vicinity of Cairo, although but little known 

 to European visitors, and still less to the Arabs in general, a pet- 



