1862.] 51 



furnish available data; nor does he admit the formation of the 

 channel between England and France in the calculation ; and he gives 

 reasons to show that this channel is of older date than generally as- 

 sumed, and that the separation existed at the time of the high-level 

 gravels, and had attained somewhat of its present dimensions at the 

 time of the newer gravels. Most of the land and freshwater shells 

 and the Mammalia had crossed over at a period anterior to this ; 

 and, as even now at the Island of Saghaleen in lat. 52 N., the 

 narrow strait freezing during the winter would admit of the passage 

 of large land animals and man during the cold periods following the 

 more extreme glacial conditions. 



The author, however, suggests two new modes by which he con- 

 ceives that eventually some approximate and more exact estimate 

 may be made both of the age of the high-level gravels and of the 

 lapse of time since the extreme glacial period, and embracing there- 

 fore the several periods under consideration. At present the evidence 

 is only sufficient to indicate the possibilities of the problem, but it 

 will need many years of careful observation before sufficient data can 

 be obtained for accurate calculation. 



1st. With the high-level gravels there are connected a number of 

 sand and gravel pipes perforating the underlying chalk to the depths 

 generally of from 5 to 50 feet, and from 1 to 10 feet wide, or more, 

 As these are caused by the slow action of carbonic acid in the water 

 gradually percolating through the overlying porous beds, dissolving 

 the chalk or other calcareous strata, and gradually letting down the 

 superincumbent drift, it is evident that if the rate of solution and 

 removal can be determined, one element for the calculation of a cer- 

 tain period will be obtained. In this various meteorological questions 

 will have to be considered. 



2nd. In conducting observations on the temperature of deep mines, 

 wells, &c., certain discrepancies in the increment of heat at increas- 

 ing depths and at different places have been noticed. No explana- 

 tion of these anomalies has been offered. The author suggests that 

 they may arise from disturbing causes originating with a former 

 period of intense cold. At Yakutsk, where the ground is now frozen 

 to a depth of 382 feet, the permanent line of 53 Fahr. would, taking 

 at an average an increase of 1 for every 60 feet, be found at a depth 

 of 1642 feet. If, from some geological change, the mean tempera- 



E 2 



