TRANSxVCTlONS OF THE SECTIONS. 77 



time. Now we are brought by pbj'sicists like Sir W. Thomson and Captain Datt'in 

 to face the question, Is there evidence of such earlier masses of stratitied de- 

 posits ? If we allow to the physical argument all the weight to which its advo- 

 cates deem it entitled, if we accept 15 millions of years, nay, even if we admit 

 100 millions of years as our limit, it follows that we may still regard the earth as 

 in its first stage of cooling. But when we turn to the geological evidence, all that 

 can be advanced is that the Laurentian strata contain fragments presumably derived 

 from earlier strata ; but metamorphosed fragments among metamorphic rocks are 

 not the most reliable guides, and there is the positive evidence that the Laurentian 

 area has not been covered to any extent, if at all, by later deposits. So far as 

 direct proof goes, therefore, we have none that the earliest known stratified rocks 

 are not also the earliest deposited after cooling. Even if we disregard the limits 

 imposed by the philosophers, liberal though they ai'e in Sir W. Thomson's hands, 

 the absence of proof that later deposits covered Lam-entian areas seems entitled 

 to greater weight than is usually allowed to negative evidence. At best the asser- 

 tion of antecedent strata is an arbitrary one, which any of us is at liberty to con- 

 tradict, and in favour of which no pliysical evidence, and only zoological prejudices 

 can be adduced. The earliest stratified deposits known are the Laurentian ; and 

 they are, so far as we know, the earliest to have been deposited. 



But apart from these possible though improbable earlier deposits, geological 

 time is said to be lengthened by the missing strata of later periods. Mr. Croll has 

 given great prominence to this, which is another of the things taken for granted in 

 geology. Commenting on Mr. Huxley's remark that if deposit went on at the 

 rate of 1 foot for 1000 years, the 100,000 feet of strata assumed by him to form the 

 earth's crust would be laid down in the 100 millions of years which Sir W. Thom- 

 son had given as the limit, "But," sajs Mr. Croll, "what of the missing strata?" It 

 is commonly said that we have only a part of the deposits of any period, that the 

 last have been denuded awaj', and that thus the time needed for their deposit and 

 for their subsequent removal are out of our knowledge. This is based on what we 

 see on the shore when the tide rises and falls and washes oft' at each turn a part of 

 the sand and mud laid down in the intei'val. But the older deposits were laid 

 down in deeper water than that between tide-marks, and were for the most part 

 laid down during subsidence. Even admitting removal of part of the strata to 

 have taken place dm-ing re-emergence, the quantity so withdrawu cannot be proved 

 to represent more than a small fraction of the total. To provide the needed elon- 

 gation of geological time by an appeal to arbitrary speculations is not admissible. 

 Belief on belief is, as Butler says, bad heraldrj-. The denudation to which im- 

 portance is justly ascribed is that represented by an unconformity. Re-elevation 

 lias been accompanied by disturbance of the area from a dift'erent centre than that 

 around which subsidence took place. The strata are worn obliquely; and thus 

 thickness of the mass at one place is greatly diminished, though it does not follow 

 in all cases that the maximum thickness of the strata has been affected. 



The importance — as I deem it, the excessive importance which is attached to the 

 missing strata is asserted by biologists, who apparently unconsciously seek to gain, 

 by prolonging the interval between successive groups, the time which ought rather 

 to be sought for in tracing, were that possible, the migrations of the species which 

 seem to have suddenly died out. In otlier words, there is a reversion to the older 

 ideas regarding the succession of strata which are embodied in such phrases as 

 the Age of Fishes, the Age of Eeptiles, and the like. 



But the inequality of surface which unconformitj' involves, entails that other 

 consequence, that the maximum thicknesses of the two masses of deposits do not 

 coincide in position. Hence the thickness of the strata in the area will be exag- 

 gerated, the time spent in deposit also exaggerated, if the two thicknesses f re put 

 together. This has been done by Mr. Darwin in drawing inferences from the mea- 

 surements given him by Prof. Ranisaj', measurejuents which, on the face of them, 

 do not represent a continuous pile of rock. Mr. Darwin nssunies either that ihe 

 Welsh hills ("not to speak of the Hebrides) were covered by all the later strata 

 now demuled — or that if we sunk a bore, say on the erst coast, we should go 

 through the whole series as tabulated. "\Mieu Prof. Huxley took 100,000 feet as 

 the thickness of the sedimentai-y series, tlie same notion was unconsciously present, 



