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ANNIVEESAEY ADDRESS 



assumes a vortex motion. This may be seen if you inject a 

 coloured fluid into water ; also if you watch the curling; smoke 

 from the mouth of a smoker, or the steam from a locomotive steam- 

 engine. 



Geology furnishes many examples of the circulation of matter. 

 As you drive along the narrow lanes of Hertfordshire after the 

 roads have been recently repaired, you will see the road-maker throw 

 some large round stones on one side ; they are smooth and water- 

 worn, and if you break them you will find they are not composed 

 of flint but of some rock that must have come from a distance. 

 They are considered to show the action of ice, and that the period 

 in which they were transported to Hertfordshire was one of 

 extreme cold —in fact, a glacial period. At Busliey, a short dis- 

 tance from "Watford, you will find the clay of the London Basin ; 

 and in this London Clay, numerous shells, Nautili and others, are 

 found, which clearly indicate a hot climate. We have therefore 

 within a short distance indications of a tropical and also of an arctic 

 climate. We also find in the present day in the Arctic Regions, 

 fossil remains of a vegetation that could not possibly have grown 

 in the climate at present existing there. If this only occurred once, 

 we might suppose that the earth was formerly much hotter than it is 

 now, and that it is gradually cooling. But we find, in fact, a suc- 

 cession of hot and of cold climates, and the climate of Watford is 

 much warmer now than it was when the boulders were brought 

 here on ice ; and I think that the sun and the earth cannot be 

 gradually cooling, and may be getting hotter. 



I will not detain you by enumerating the numerous theories 

 which have been advanced to account for the changes of climate in 

 the same places on the earth. Our late President, Mr. John Evans, 

 has propounded a theory before the Royal Society, which he has 

 also brought forward in his address as Pi-esident of the Geological 

 Society. Several theories that I have heard of to account for 

 change of climate have this defect — they are occasional and 

 extraordinary, and might possibly account for one change. But 

 we have to account for an alternation of hot and of cold periods. 

 Mr. James Geikie says in his last work, ' The Great Ice Age,' 

 " All the geological formations, except the Laurentian, have been 

 considered to yield evidence, more or less satisfactory, of the 

 foi-mer action of ice." Therefore we have to account for a series 

 of alternating geological periods of summer and winter on the earth. 



When we call the last glacial period the Great Ice Age, we do 

 not infer that it is any greater than the ice periods which preceded 

 it, only that, being the last, the evidence of it is more marked. 



