TRANSACTIONS OF SECTION C. 



729 



dinavia, where all the zones recognised in the British series are represented by a 

 column of sediment 290 feet in thickness. If 1,600,000 years be a correct 

 estimate of the duration of Cambrian time, then each foot of the Scandinavian 

 strata must have occupied 5,ul3 years in its formation. Are these figures 

 sufficiently inconceivable ? 



In the succeeding system, that of the Ordovician, the maximum thickness is 

 17,000 feet. Its deposits are distributed over a wider area than the Cambrian, 

 but they also occupied longer time in tbeir formation ; hence the area from 

 which they were derived need not necessarily have been larger than tbat of the 

 preceding period. 



Great changes inthe geography of our area ushered in the Silurian system : its 

 maximum thickness is found over the Lake district, and amounts to 15,000 feet ; 



Fig. 2.— Chart of the distribution of land and sea, and of the thickness of deposits of 

 the Cambrian system. The dotted lines indicate distances of 100 and 200 

 miles from the shore. 



but in the little island of Gothland, where all the subdivisions of the system, from 

 the Landovery to the Upper Ludlow, occur in complete sequence, the thickness is 

 only 208 feet. In Gothland, therefore, according to our computation, the rate of 

 accumulation was one foot in 7,211 years. 



With this example we must conclude, merely adding that the same story is 

 told by other systems and other countries, and that, so far as my investigations 

 have extended, I can find no evidence which would suggest an extension of the 

 estimate I have proposed. Ifc is but an estimate, and those who have made 

 acquaintance with ' estimates ' in the practical affairs of life will know how far 

 this kind of computation may guide us to or from the truth. 



This Address is already unduly long, and yet not long enough for the magni- 

 tude of the subject of which it treats. As we glance backwards over the past we 



