September 13, 1900] 



NATURE 



489 



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 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 affect the maximum thick- 

 ness 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 greater magnitude and fre- 

 quency 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 recog- 

 nised in the Palteozoic systems. Thus we are compelled to 

 treat our rate of deposition as uniform, notwithstanding the 

 serious error this may involve. 



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, re- 

 presenting the distribution of land and 

 sea over the European area during the 

 Cambrian period. The strata of this 

 system attain their maximum thick- 

 ness of 12,000 feet in Merionethshire, 

 Wales ; they rapidly thin out north- 

 wards, and are absent in Anglesey ; 

 scarcely less rapidly towards Shrop- 

 shire, where they are 3000 feet thick ; 

 still a little less rapidly towards the 

 Malverns, where they are only 800 

 feet thick ; and most slowly towards 

 St. David's Head, where they are 

 7400 feet thick. The Cambrian rocks 

 of Wales were in all probability the 

 deposits of a river system which 

 drained some vanished land once 

 situated to the west. How great was 

 the extent of this land none can say ; 

 some geologists imagine it to have 

 obliterated the whole or greater part 

 of the North Atlantic Ocean. For 

 my part I am content with a some- 

 what large island. What area of this 

 island, we may ask, would suffice to 

 supply the Cambrian sediments of 

 Wales and Shropshire ? Admitting 

 that the area of denudation was ten 

 times as large as the area of deposi- 

 tion, its dimensions are indicated by 

 the figure a b c d on the chart. This 

 evidently leaves room enough on the 

 island to furnish all the other deposits 

 which are distributed along the west- 

 ern shores of the Cambrian Sea, while 



those on the east are amply 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 dis- 

 appoint 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 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 5513 years in its 

 formation. Are these figures sufficiently inconceivable ? 



In the succeeding system, that of the Ordovician, the maxi 

 mum thickness is 1 7,000 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, accord- 



ing to our computation, the rate of accumulation wa.s one foot 

 in 721 1 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 

 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 magnitude of the subject of which it treats. As we 

 glance backwards over the past we see catastrophism yield to 

 uniformitarianism, and this to evolution, but each as it disappears 

 leaves behind some precious residue of truth. For the future of 

 our science our ambition is that which inspired the closing words 

 of your last President's Address, that it may become more ex- 

 perimental and exact. Our present watchword is Evolution. 

 May our next be Measurement and Experiment, Experiment 

 and Measurement. 



NO. 



611, VOL. 62] 



Chart of the distribution of land and sea, and of the thickness of deposits of the Cambriaiv. 

 system. The dotted lines indicate distances of 100 and 200 miles from the shore. 



NOTES. 



Another of those disastrous hurricanes which occasionally 



visit the West Indies and United States at this season of the 



year has to be recorded. On the 8th inst. a storm of great 



violence struck the coasts of Louisiana and Texas, andj owing 



to the thickly populated districts over which it swept and to the 



high water wave which accompanied it, immense destruction to 



property and lamentable loss of life ensued. The fury of the 



j storm is said to have been felt for at least a hundred miles 



i inland, but up to the present time scarcely any details have 



arrived as to its character and the exact path that it followed. 



This part of America is one of the three regions referred to in 



; the works of Prof. W. M. Davis from which tropical storms 



I move into temperate latitudes in the northern hemisphere ; but 



we must wait for further details before it can be stated whether 



the one in question was of the nature of a tornado, which differs 



from an ordinary hurricane chiefly in its excessive violence over 



j a small, instead of a large, area. From the description so far 



