266 SCIENCE PROGRESS 



fossil forms in the pre-Cambrian. Although a very considerable 

 bulk of pre-Cambrian rock has been examined, the remains of 

 life are few and far between. In the Torridon sandstone, laid 

 down under the calm and peaceful conditions so graphically 

 described by Sir Archibald Geikie, 1 no fossils have been found. 

 Crustacea have been found in the Proterozoic. There is a lime- 

 stone deposit, which may or may not be organic, at the base of 

 the Huronian, but the comparative scarcity of life is a striking 

 and interesting fact. There is no evidence of metamorphism, 

 and there is no apparent reason why fossils should not have 

 been found. Though reasoning from the absence of such remains 

 is a very risky proceeding, the contrast between this scarcity 

 and the relative abundance in later strata at any rate suggests 

 the probability that the known forms of life were then local and 

 in process of establishment as world-wide types. If this were 

 so, it is easy to point out that the relatively rapid change of con- 

 ditions connoted by our hypothesis is a strong presumption in 

 favour of a rapid process of evolution. 



There are one or two other speculations to account for this 

 interesting fact. One is that the early seas were acid, and that 

 the organisms were therefore unable to form protective coatings 

 by the secretion of carbonate of lime. The very early date of 

 some limestone deposits will require explanation on this hypo- 

 thesis. If the speculation were accurate, lime deposition could 

 only take place locally in lakes when the process of deposition 

 had gone far enough to neutralise the prevailing acid, or, when 

 such lakes had not been part of the sea, in places where the 

 influx of the rivers would not be neutralised by the acid of the 

 sea. The speculation is somewhat wild, but some light would 

 be thrown on it if and when we have discovered whether or no 

 the earliest limestone deposits are invariably lacustrine. 



Whether this or some other reason be the explanation, it is 

 interesting to note that a very considerable proportion of such 

 pre-Cambrian fossils as have been discovered are chitinous 

 rather than calcareous ; and whether this fact be due to deficiency 

 in carbonate of lime, or whether it be due to the fact that the 

 species at that time had not acquired what has been described 

 as the lime habit, the facts point to the probability of a com- 

 paratively rapid pre-Cambrian evolution. Whether or no the 

 reasons that have been given are sufficient, it will be generally 

 1 See address to British Association, 1899. 



