ADDRESS SECTION A, B.A. 1876. 239 



tively small area, where hot springs and perhaps 

 also sulphurous vapours prove an intimate rela- 

 tionship to volcanic quality. It is worthy of 

 remark in passing that, so far as we know at 

 present, there are no localities of exceptionally 

 small rate of augmentation of underground tem- 

 perature, and none where temperature diminishes 

 at any time through any considerable depth down- 

 wards below the stratum sensibly influenced by 

 summer heat and winter cold. Any considerable 

 area of the earth of, say, not less than a kilo- 

 metre in any horizontal diameter, which for several 

 thousand years had been covered by snow or ice, 

 and from which the ice had melted away and left 

 an average surface temperature of 1 3 cent., would, 

 during 900 years, show a decreasing temperature 

 for some depth clown from the surface ; and 3600 

 years after the clearing away of the ice would still 

 show residual effect of the ancient cold, in a half 

 rate of augmentation of temperature downwards 

 in the upper strata, gradually increasing to the 

 whole normal rate, which would be sensibly 

 reached at a depth of 600 metres. 



