PRESIDENT^ ADDRESS. 31 



portion is concerned, and grinding a good deal of the higher 

 decomposed rock into clay, while the weight of the super- 

 imposed ice, the accumulation of many years, planed off the 

 hill slopes and disturbed the rocks. 



Next came a period of comparative heat, a great melting 

 of the ice in successive summers and re-glaciation in successive 

 winters washing down clay and sand from the decomposed 

 rock, filling up hollows and the interstices of the rubble of the 

 cliffs, spreading it out over the planed rocks, filling up the 

 lower valleys, in fact, using an immense mass of decomposed 

 material left on the top of the island by the sea to cover over 

 all the lower levels with sand and clay. This, supposing that 

 it is found consistent with the facts, accounts well for the local 

 character of the clay, so firmly held to by Mr. Derrick, for 

 the presence of pebbles in the clay, washed down from a 

 higher level, for the presence of clay in the upper raised 

 beaches, and for the " talus " like look of some of the beach 

 deposits, the latter having been redistributed or moved by the 

 rush of local waters. 



I do not wish to do more than indicate the probable line 

 that our thought will take, nor do I wish to say that the 

 explanation here offered must be the correct one. We are a 

 scientific society, and as such must judge by the evidence 

 before us only; at the same time, while using theories to assist 

 us in the collection of evidence, we must be free to move from 

 one theory to another, as the evidence demands, using our 

 theories only as stepping-stones, useful as long as they fasten 

 us to a forward course, but not to be blindly adhered to in the 

 face of contrary knowledge. 



One point more and I have done. The more I think of 

 the clays and their peculiarities the more I see that some 

 explanation must be worked out. The first point to be men- 

 tioned is that there is always a well-marked line of separation 

 between the deposit and the decomposed rock. I know that 

 in this statement I have Mr. Derrick against me,* and that 

 he thinks that they pass the one into the other. I have re- 

 examined many places lately and am conviuced that there is 

 always a line to be seen where vegetation has not interfered. 

 Again, we have the great depth to consider. We have 

 measured 14 feet at the Forest, 20 feet at the Vale, behind 

 Delancey Hill, and even 30 feet beyond the last named. In 

 the Yale the clay rests on previous sandy deposits as well as 

 on decomposed rock. Now it seems to me that a purely local 

 origin is not consistent with the great depth any more than 

 * Transactions for 1892, pp. 212-218. 



