534 



NA TURE 



[April 4, 1895 



uniform and the same as that of the present, this 

 thickness of rock would have required a period of 

 1,526,750,000 years for its accumulation. Dr. Haughton 

 is not a uniformitarian, consequently he divided this 

 number by lo. Dr. Wallace next made what must be 

 considered a great step in advance, by pointing out that 

 the sediment which is carried into the sea is not de- 

 posited uniformly over the whole sea-floor, but, as the 

 Challenger dredgings clearly showed, along a compara- 

 tively narrow marginal tract. Instead, therefore, of 

 multiplying :;i^jjj (the yearly rate of denudation) by ,',-., 

 he divided it by ,V (the proportion of the area of maxi- 

 mum deposition to the area of denudation), and thus 

 obtained 2S millions as the number of years required for 

 the accumulation of 177,000 feet of rock. 



A further correction was next made by Mr. C. Davison, 

 who showed that the fraction ^un.cr 's obtained by an 

 error in arithmetic, and that the true value is .^^^u- In- 

 troducing this fraction into Mr. Wallace's calculation, we 

 obtain in round numbers 22 millions of years, a close 

 approximation to the result, deduced from physical 

 considerations, by Mr. Clarence King. 



Of late years considerable additions have been made 

 to our knowledge of the thickness of the systems of 

 stratified rock, and 1 present the following table as 

 representing the maximum thickness of all known 

 formations down to the base of the Cambrian, a definite 

 horizon marked, as is well known by the occurrence of 

 fossil remains of most of the great subdivisions of the 

 Invertebrata : — 



System. 

 Cambrian ... 

 Ordovician 

 Silurian 

 Devonian ... 

 Carboniferous 

 Permian ... 

 Trias 

 Jurassic 

 Cretaceous 

 Eocene 

 Oligocene 

 Miocene ... 

 Pliocene ... 



Thickness in feet. 



16,000 



14,000 



14,000 



20,000 



21,000 



12,000 



13,000 



8,000 



14,000 



12,000 



12 000 



6,000 



2,000 



164,000 



First appearance of 



Fish 



Amphibians 



Reptiles 



Mainmals 



Eulheria 



The total thickness is 164,000 feet, lying in a fairly 

 continuous series, and calculating by Mr. Wallace's 

 method, this leads to the conclusion that, in round 

 numbers, 21 millions of years have elapsed since the begin- 

 ning of Cambrian times. The truth of Mr. Wallace's 

 argument depends on the assumption that an area of 

 maximum deposition retains a constant position during 

 the existence of a geological system. This is no doubt 

 approximately the case, but so far as it is not, the devia- 

 tion from stability will render Mr. Wallace's estimate 

 deficient. On the other hand, as Mr. Wallace himself 

 recognised, the area of maximum deposition does not 

 extend uniformly round the coast line, but is concentrated, 

 if one may so speak, near the mouths of rivers : the 

 effect of taking this into account will far more than 

 compensate for any shifting of the area. It is unnecessary 

 to do more than point out that deposits, where they 

 attain their maximum thickness, are of a more or less 

 deltaic nature, and were probably deposited near the 

 mouth of large rivers, in seas more or less land-locked. 

 From investigations in which 1 am now engaged, 1 am 

 led to conclude that where systems attain their maximum 

 thickness, accumulation may have proceeded at the rate 

 of one foot in a century, or even more rapidly. 



The question largely depends on the relative size of 

 areas of denudation and deposition : an objector to 

 my estimate may urge that accumulation at this rate 

 involves the existence of areas of denudation of much 



NO. 1327, VOL. 51] 



'arger dimensions than the map will find room for. It 

 is worth while to inquire into this, and a single ex.imple 

 will suffice. Let us consider the coal measures of the 

 British Isles. Suppose they cover, to the depth of 

 half a mile, a circular area 300 miles in radius, having its 

 centre somewhere over Anglesey, their volume will thus 

 be 141,372 cubic miles ; add to this 15,876 cubic miles for 

 the deposits of greater thickness occurring over the North 

 of England, and South Wales and Somersetshire. This 

 gives a total thickness of 157,248 cubic miles. But since 

 the maximum thickness is 12,000 feet, these will have 

 accumulated, according to our assumption of i foot in a 

 century, in 1,200,000 years. The coexistent area of de- 

 nudation affords ,_. |\yj7 of a foot of sediment per annum, 

 or oooooooS cubic mile per square mile yearly. In 

 1,200,000 years this will amount to nearly ,'„ cubic mile 

 per square mile ; and thus the 157,248 cubic miles of sedi- 

 ment Ml the coal measures will have required a land surface 

 1.572,480 square miles in area for their supply. This will 

 be represented by a circular area with a radius of 707' 

 miles, and that an area of land several times these dimen- 

 sions may have existed north and west of the British 

 Isles during carboniferous times, is an assertion which 

 most geologists will be prepared to defend. 



So far as I can at present sec, the lapse of time since 

 the beginning of the Cambrian system is probably 

 less than seventeen millions of years, even when 

 computed on an assumption of uniformity, which to me 

 seems contradicted by the most salient facts of geology. 

 Whatever .additional time the calculations made on 

 physical data can afford us, may go to the account of Pre- 

 Cambrian deposits, of which at present we know too- 

 little to serve for an independent estimate. 



No one can regard without satisfaction the introduction 

 into Lord Kelvin s argument of well-ascertained data as 

 regards the melting points and other properties of rocks. 

 Dr. Joly finds the melting point of basalt to be even 

 lower than that of diabase, viz. 815' C, a result ii» 

 accordance with that found by other investigators. 

 These facts, though of great assistance in supporting the 

 short chronologists of the earth's age, may prove- 

 embarrassing when the question of the physical state of 

 the interior of the earth is ready for reconsideration. 

 Dr. Joly finds the value of d/jilp for basalt to be 

 o'oo6, and for diabase, according to Carl Baru5, it is 

 0021 at 1 200' C. ; in either case the temperature gradient 

 gains on the melting point gradient rapidly enough to 

 show that, at no great distance beneath the surface of 

 the earth, the interior, if it consist of such rocks as 

 these, is in a state of liciuidity. Cleologists in general 

 would probably be glad to purchase an internal liquid 

 shell at a cost of several millions of years. WouUl not, 

 however, the admission of the existence of li(|ui<l shells 

 in the interior of the earth, deprive the mathematical 

 argument, as at present formulated, of all validity.' 



W. J. SOI.LAS. 



THE ANNIVERSARY OF THE CHEMICAL 

 SOCIETY. 



"T^HE anniversary meeting of the Chemical Society 

 -•- was held at the .Society's rooms, on Wednesday 

 March 27, when the following officers and Council were 

 elected : — 



President, Dr. A. O. Vernon Ilarcourt, ]•'. K.S. Vice- 

 Presidents (who have filled the office of President), .Sir F. A. 

 Abel, K.C.H., F.R.S., Dr. H. E. ArmstronK, F.R.S., Dr. A. 

 Crum Brown, F.K.S., W. Crookes, F.K.S., Dr. E. Frankland, 

 F.R.S., SirJ. II. Gilbert, F.R.S., Dr. I. II. Gladstone, F.R.S., 

 Dr. n. Midler, F.R..S., VV. OdIinK," F.R.S., Dr. W. H. 

 Perkin, F.R.S., Lord Playf.iir, K.C.B., F.R.S., Sir II. K. I 

 Roscoe, F.R.S., Dr. W. J. Russell, F.R..S., and Dr. A. W. ' 

 Williamson, F.R.S. Vice-Presidents Dr. E. Atkinson,' 

 Iloriice T. lirown, F.R.S., Prof. F. R. Japp, F.R.S., Lud*lg 



