SLOW DEPOSITION 43 



provided for by that portion of the European continent 

 which then stood above water. 



If one foot in a century be a quantity so small as to 

 disappoint the imagination of its accustomed exercise, let 

 us turn to the Cambrian succession of Scandinavia, where 

 all the zones recognised in the British series are repre- 

 sented 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 5,513 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 their formation ; 

 hence the area from which they were derived need not 

 necessarily have been larger than that of the preceding 

 period. 



Great changes in the geography of our area ushered in 

 the Silurian system : its maximum thickness is found 

 over the Lake district, and amounts to 15,000 feet ; 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. It 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. 



