NOVEMBBK 23, 1900.] 



SCIENCE. 



79 



of increase is six feet in a century, which 

 might perhaps correspond to one foot of 

 coal in the same period. 



The rate of deposition has been taken as 

 uniform through the whole period of time 

 recorded by stratified rocks; but lest it 

 should be supposed that this involves a 

 tacit admission of uniformity, I hasten to 

 explain that in this matter we have no 

 choice ; we may feel convinced that the rate 

 has varied from time to time, but in what 

 direction, or to what extent, it is impossible 



the greater magnitude and frequency of the 

 tides, and thus while larger quantities of 

 sediment might be delivered into the sea, 

 they would be distributed over wider areas, 

 and the difference between the maximum 

 and average thickness of deposits would 

 consequently be diminished. Indications 

 of such a wider distribution may perhaps 

 be recognized in the Paleozoic systems. 

 Thus we are compelled to treat our rate of 

 deposition as uniform, notwithstanding the 

 serious error this may involve. 



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. 



to conjecture. That the sun was once much 

 hotter is probable, but equally so that at an 

 earlier period it was much colder ; and 

 even if in its youth all the activities of our 

 planet were enhanced, this fact might not 

 aflfect the maximum thickness of deposits. 

 An increase in the radiation of the sun, 

 while it would stimulate all the powers of 

 subaerial denudation, would also produce 

 stronger winds and marine currents ; 

 stronger currents would also result from 



The reasonableness of our estimate will 

 perhaps best appear from a few applications. 

 Fig. 2 is a chart, based on a map by De 

 Lapparent, representing the distribution of 

 land and sea over the European area during 

 the Cambrian period. The strata of this 

 system attain their maximum thickness of 

 12,000 feet in Merionethshire, Wales ; they 

 rapidly thin out northwards, and are ab- 

 sent in Anglesey ; scarcely less rapidly to- 

 wards Shropshire, where they are 3,000 feet 



