The Scottish Naturalist. 101 



facts that tests and establishes or invalidates the soundness of 

 any scientific theory. Does polarity stand that test? I have 

 not been able to make an investigation* of the recent additions 

 to Palaeontology adequate enough, and am therefore not able 

 to speak with assurance. 'I observe that Mr. Wallace, who 

 republishes last year the explanation he suggested seventeen 

 years ago, of the facts of which polarity professes to be an expres- 

 sion, appends no note to the effect that the facts have assumed 

 in these years any other form of arrangement. And so far as 

 I know their polar arrangements still stands much as it did. 

 Great additions to fossil genera have been made ; and notably 

 to Triassic genera from the St. Cassian beds in the Austrian 

 Alps, as well as those of the oldest periods by Barrande's 

 researches. But I have seen nothing that forbids the conclu- 

 sion that the earliest Palaeozoic and the latest Neozoic for- 

 mations have on the whole been the greatest gainers, and still 

 show as much as ever, two maxima of generic development. 

 It may be noted that the fact of the Silurian maximum main- 

 taining its place goes to weaken any objection for negative 

 evidence and to corroborate the truly representative character 

 of the ascertained facts. 



Besides the growth of Palaeontological facts, it may also be 

 objected that the advance in physical geology bears most un- 

 favourably on this polar idea. The one of the extremes of the 

 geological series with which it deals, the Tertiary, remains, of 

 course where it was, but what was the other pole has, through 

 the hammer of the geologist and his speculations together, re- 

 ceded immensely farther back ; so that Cambria and Siluria 

 may now stand chronologically about the middle of the fossili 

 ferous deposits, or what have been so, instead of being the ear- 

 liest. " If the theory of natural selection be true/' says Darwin, 

 " it is indisputable that before the earliest Cambrian stratum 

 was deposited, long periods elapsed, as long as, or probably far 

 longer than, the whole interval from the Cambrian age to the 

 present day; and that during these vast periods the world 

 swarmed with living creatures." Yet, at the worst, we may 

 take the Silurian as the completion of the first cycle of the 

 earth's course of evolution, the time and the whole state of 

 things, in which the characteristic agencies and conditions of 

 that cycle had reached their goal. It is the results of the earliest 



