SCIENCE-GOSSIP. 



5i 



THE LOWER CAMBRIAN SERIES 



With some Suggestions. By Alexander Ramsay. 



IN this paper on Lower Cambrian geology 

 attention will be mainly restricted to the 

 various ways in which the ages of the strata can 

 be determined both relatively and, in a rough 

 approximate way, absolutely. 



In dealing with geological subjects, it seems 

 to me that the general tendency of authors has 

 been to rely too exclusively on the stratigraphical 

 superposition of fossils as a test of age. This 

 evidence is unquestionably of high value ; yet it 

 seems desirable that the age should be based on 

 a series of independent criteria rather than on 

 one which is almost entirely unchecked. 



As an illustration of what I mean, I will take a 

 case haphazard. In the Tenth Annual Report of 

 the U.S. Geol. Survey, 1890, p. 596, Mr. C. D. 

 Walcott says: "The presence of the Olenellus 

 fauna is chiefly relied on as indicative of the 

 L. Cambrian, not that it is considered to be strictly 

 contemporaneous, but geologically only. Its wide 

 range is evidence that it was of precisely the same 

 age in all localities." 



If it be assumed that Olenellus and the fauna 

 associated with it is of L. Cambrian age (as under- 

 stood by Mr. Walcott, and equivalent to my 

 eons, 116 to 112) then any strata containing them 

 must be assigned to this age and no other. I do 

 not wish to question the accuracy of the 

 conclusion ; but it certainly seems to me to be an 

 unsafe position to maintain that Olenellus is 

 necessarily excluded from all beds not of this age. 

 It requires strengthening by independent evidence 

 of some kind. 



As this independent evidence is, I apprehend, a 

 great desideratum, I will endeavour to suggest various 

 independent ways of testing the age of strata, and to 

 exemplify these by illustrations drawn from the 

 L. Cambrian period. The reliability of each may 

 be more or less doubtful, and the isolated con- 

 clusions may be of little value. If, however, two or 

 three or more of them should point to a similar 

 conclusion, such coincident conclusion must be, I 

 consider, of more value than one based solely on 

 the stratigraphical superposition of fossils. The 

 reliability of this last criterion is not gainsaid 

 when applied locally ; it is the general application 

 of it which is considered to be illogical. 



A full account of the lines of evidence I propose 

 to rely upon belongs to the subject of geology 

 generally, and therefore a mere summary is all 

 that can be given here. These lines of evidence 

 may be grouped into two divisions ; viz. (1) those 

 which are, by implication, of a more or less 



continuous nature ; and (2) those which are 

 intermittent, but of wide geographical extent ; 

 the most useful of the latter being such as are of 

 short duration. 



The continuous division comprises (1) the physi- 

 cal, and (2) the biological phenomena. 



The physical continuous group is mainly repre- 

 sented by the inferred rate of deposition based upon 

 all the facts obtainable as to the rates of all the 

 collateral phenomena, such as the intensity of 

 climate, elevation of land, denudation and currents. 

 It is believed that all these have been, more or less, 

 in continuous activity, and that their main visible 

 result is represented by the strata already dis- 

 covered. These strata, as I consider, afford 

 sufficient material for estimating the aggregate 

 thickness of the geological continuous succession 

 of deposits, as also the total mass. The figures 

 thus arrived at, taken in conjunction with the pre- 

 sumed average, afford the means of inferring both 

 the relative ages and the approximate absolute 

 time value of the strata. There is no doubt such 

 calculations are open to objections, but, however 

 faulty they may prove to be, they will serve pro- 

 visionally as counterchecks on other methods of 

 determining the relative and absolute ages of 

 stratified deposits. 



The biological continuous division is mainly 

 represented by the inferred rate of change in 

 animal organisms. The evidence already afforded 

 by fossils suffices, in my opinion, to show clearly 

 that there has been, in the main, a progressive 

 advance in organization from the oldest times 

 onward. When the rate of this change has been 

 determined, it will afford another and independent 

 means of fixing the ages of strata. This general 

 rate, which finds its expression in what I would 

 term the organic grade of the fossils, may be itself 

 checked by numerous subsidiary grades, for it is 

 manifest that life forms have progressed (and in 

 some cases have retrogressed) as a collection of 

 organs rather than as individuals. The change 

 may be forward or backward in generic and other 

 groups, and it may be forward or backward as 

 regards one or more systems of organs. Isolated 

 facts relating to these often supply the means for 

 constructing a scale. 



Many of these minor scales will appertain to the 

 intermittent class of phenomena, but will rarely be 

 applicable to the purpose for which they are 

 especially useful. That purpose is to serve as a 

 check on the time values deduced from local 

 phenomena in places distant from each other. An 



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