REPORT OF MEETINGS FOR 1902 235 



and that the rivers which transported these materials seaward 

 spread the wasted material out over an area equal to that 

 whence the material was derived. Taking this area as a 

 whole, therefore, on this supposition, each foot of the strata, 

 averaging the whole from top to bottom, required three 

 thousand years to form. It is certainly not very safe to 

 make calculations based upon data which at the best can hardly 

 be regarded as satisfactory when taken alone, and without 

 some confirmatory evidence. But it happens that the Silurian 

 Eocks are fossilif erous almost throughout, and a careful study 

 of their fossils assures us that so many changes in the marine 

 life of the period ensued in the time in question that one 

 cannot help feeling that the 3000 years X 12,000 (the thickness 

 in feet), thirty six millions of years is quite inadequate to 

 account for the many changes in the organic world that 

 ensued. During the last three millions of years hardly any 

 changes have taken place in the plants or animals of western 

 Europe, except in the case of the larger mammalia.* If 

 we take this, as most biologists would do, as any guide to 

 the rate of change in the organic world in past times, what 

 are we to say regarding the extensive and important changes 

 in even the lower forms of life which ensued during the Silurian 

 Period ? I shall, therefore, set the interval of time in question 

 at 36,100,000 years. 



Next we have to take into account the time implied by 

 the crumpling, upheaval, and subsequent waste, none of 

 which commenced until the last of the Silurian Eocks (and 

 perhaps also the Lanarkian rocks as well) had been formed. 

 The only data we have, which we can use for this, are those 

 relating to the rate of waste. Now, in this case, seeing that 

 there is some difference of opinion between my colleagues 

 and me with regard to the thickness of the Silurian Eocks 

 of the South of Scotland, I do not feel justified in asking 

 others to accept my estimate of that thickness in dealing with a 

 question like this. I will, therefore, base that estimate upon 

 the assumption that the thickness of Silurian Eocks which 

 formerly overlay the Gala Eocks of the Siccar Point was four 



* See Goodcbild, Origin of the British Flora, Proc. Bot. 8oc. Edin. 

 (1902.) 



