114 Dr Richardson on the Frozen Soil of North America. 



fields of ice in its neighbourhood for nearly the whole summer, 

 resulting from the form of the land, and the direction of the 

 prevailing winds and currents of the sea. 



As to the local influence of soil to which Professor Baer 

 directs our attention, I have been informed by a gentleman 

 who has had forty years' experience as a practical farmer in 

 England, that when he used sand as a covering for potatoes, 

 carrots, or other vegetables, in the winter, the frost penetrated 

 farther than when loam or other earth was used, and that the 

 looser the latter was thrown over the vegetables, the better 

 was the protection it afforded. He remarked, also, that he 

 always found the earth frozen to a greater depth after severe 

 frosts under a beaten footpath in a field, or compact gravel 

 on the highway, than in loose soil. 



Fort-Simpson, on the Mackenzie, being nearly in same 

 latitude with Yakutzk (62° 11' N., and 62° 1\' N.), is a de- 

 sirable locality for ascertaining the thickness of the perma- 

 nently frozen stratum. At the latter place a well has been 

 sunk into the frozen soil to the depth of 382 feet, and the 

 temperature of the earth, which was +18.5° F. at some feet 

 below the surface, gradually rose to + 31.9° F. at the bottom 

 of the well, where the soil was so loose as to require timber- 

 ing, which it had not done higher up. This gives a rise of 

 temperature equal to one degree of Fahrenheit's scale for 

 every 28| feet of descent at a place where the mean heat of 

 the year is about + 14° F.* In Phillips's Guide to Geology, 

 the mean increment of heat is stated to be 1° F. to every forty- 

 five feet of descent from the surface of the earth, which is 

 one-third less quick than the above. At Fort-Simpson the 

 mean temperature of the air is about + 25" F., and the frozen 

 soil was found to extend at least seventeen feet from the sur- 

 face. A thermometer was kept at the bottom of the pit for 

 some time, but the register of its indications has not reach- 

 ed me. Mr M c Pherson not having been made aware of the 



* >f. Erman (Geograph. Journ. viii. p. 213) states the mean heat at Ya- 

 kutsk, as deduced from observations made thrice a-day in the year 1827, to 

 be + 18.72° F. The mean stated in the text is also from M. Erman's obser- 

 vations, but continued for several years, and was found by drawing the daily 

 curve for the year indicated by the means at the specified hours.— (Geogr. 

 Journ. ix. p. 380.) 



