TRANSACTIONS OP SECTION C. 723 



we encounter reptiles and the ancestors of reptiles, probably ancestors of mammals 

 too ; then into the Carboniferous, Avhere we find amphibians, but no true reptiles ; 

 and next into the Devonian, where tish predominate, after making their earliest 

 appearance at the close of the Silurian times ; thence downwards, and the verte- 

 brata are no more found — we trace the evolution of the invertebrata alone. Thus 

 the orderly procession of organic forms follows in precisely the true phylogenetic 

 sequence: invertebrata first, then vertebrates, at tirst lish, then amphibia, next 

 reptiles, soon after mammals, of the lowlier kinds tirst, of the higher later, and 

 these in increasing complexity of structure till we finally arrive at man himself. 

 While the living world was thus unfolding into new and nobler forms, th.j 

 immutable Lunjula simply perpetuated its kind. To select it, or other species 

 equally sluggish, as the sole measure of the rate of biologic change would seem as 

 strangT a proceeding as to confound the swiftness of a river with the stagnation 

 of the pools that lie beside its banks. It is occasionally objected that the story 

 we have drawn from the palteontological record in mere myth or is founded only 

 on negative evidence. Cavils of this kind prove a double misapprehension, partly 

 .•IS to the facts, partly as to the value of negative evidence, which may be as good 

 in its way as any other kind of evidence. 



Geologists are not unaware of the pitfalls which beset negative evidence, and 

 they do not conclude trom the absence of fossils in the I'ocks which underlie the 

 Cambrian that pre-Cambrian periods were devoid of life ; on the contrary, they are 

 iully persuaded that the seas of those times M-ere teeming with a rich variety of 

 invertebrate forms. How is it that, with the exception of some few species found 

 in beds immediatelv underiving the Cambrian, these have left behind no vestige of 

 their existence ? The explanation does not lie in the nature of tbe sediments, 

 which are not unfitted for the preservation of fossils, nor in the composition of the 

 then exisiing sea water, which may have contained quite as much calcium carbonate as 

 occurs in our present oceans; and the only plausible supposition would appear to be 

 that the organisms of that time had not passed beyond the stao-e now represented 

 by the larvaj of existing invertebrata, and consequently were either unprovided 

 •with skeletons or at all events with skeletons durable enough for preservation. If 

 so, the history of the enrlier stages of the evolution of the invertebrata will receive 

 no light from pah-eontology ; and no direct answer can be expected to the question 

 whether, eighteen or nineteen millions of years being taken as sufficient for the 

 evolutionof the yertebrata, the remaining available eight millions would provide 

 for that of the invertebrate classes which are represented in the lowest Cambrian 

 deposits. On a priori grounds there would appear to be no reason why it should 

 not. If two millions of years afforded time enough for the conversion of fish into 

 amphibians, a similar period should suffice for the evolution of trilobites from 

 annelids, or of annelids from trochospheres. The step from gastrulas to trocho- 

 spheres might be accomplished in another two millions, and two millions more 

 would take us from gastrulas through morulas to protozoa. 



As things stand, biologists can have nothing to say either for or against such 

 a conclusion : they are not at present in a position to ofler independent evidence ; 

 nor can they hope to be so until they have vastly extended those promising 

 investigations which they are only now beginning to make into the rate of the 

 variation of species. 



Unexpected Absence of Thermal Me(a77io7'j)hosi8 in Ancient Rochs. 



Two difficulties now remain for discussion: one based on theories of mountain 

 chains, the other on the unaltered state of some ancient sediments. TLe latter may 

 be taken first. Professor van Hise writes as follows regarding the pre-Cambriin 

 rocks of the Lake Superior district: 'The Penokee series furnishes an instructive 

 lesson as to the depth to which rocks may be buried and yet remain but slicrhtlv 

 aflected by metamorphosis. The series itself is 14,000 feet thick. It was covered 

 before being upturned with a great thickness of Keweenaw rock. This series at 

 the Montreal Eiver is estimated to be 50,000 feet thick. Adding to this the known 

 thickness of the Penokee series, we have a thickness of 64,000 feet, . . . The 



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