10 C. Lapioorth — Classification of the Lower Palaeozoic Rocks. 



things, an unmistakable base-line for his system, capable of being 

 rigidly defined upon his maps and sections, the presence of a decided 

 unconformability affords the very thing of which he stands most in 

 need. The grouping founded upon stratigraphical breaks com- 

 mends itself to his mind with a force that is practically irresistible. 

 But it is far otherwise with the cautious systematist, who endeavours 

 to found his systems in accordance with those of Nature herself, 

 upon principles, not of local, but of universal application. Though 

 fully cognizant of the value of an unconformability as affording him 

 a fairly reliable horizon within a limited area, he soon learns that it 

 is of all things most untrustworthy when it extends over regions of 

 large diameter. It is at most a local phenomenon, wholly misleading 

 except in local application. 



It is surely a work of supererogation in these days to point out 

 how the tendency of the entire course of geological discovery for 

 the last fifty years has been to reduce to a mere shadow the magni- 

 tude of the miraculous and world-wide stratigraphical breaks that 

 bounded the geologic systems of our forefathers. The doctrine of 

 universal convulsion and the simultaneous destruction of all the life 

 upon the earth at the end of each great epoch has so long since 

 passed into the limbo of exploded hypotheses, that it would be highly 

 amusing, were it not so painful, to see its degenerate and impoverished 

 survival — the dogma of the necessity for general stratigraphical and 

 palgeontological breaks between our modern systems — dragging out 

 its miserable and ridiculous existence, even in our midst, and claiming 

 allegiance from men of standing in the science. 



One concession, and one only, appears to be all that is needful to 

 meet the real facts of the case. As a general rule, our British 

 systems have been founded, less upon palseontological than upon 

 mineralogical considerations, and it is more of the nature of a series 

 of happy accidents, than a geologic necessity, that they happen to 

 possess such distinctive faunas. In all cases, however, it is clear, 

 both here and elsewhere, that the faunas that characterize our 

 accepted rock-systems owe their distinctness — such as it is — to the 

 fact that in the more typical areas there happened to be an absence 

 of fossiliferous strata to unite them. Whether the time thus zoo- 

 logically unrepresented was occupied in the upheaval and partial 

 denudation of the rocks of the preceding system (as locally between 

 the so-called Loioer and Upper Silurians of Britain), or whether, on 

 the other hand, it was filled by the deposition of barren strata (as 

 between the corresponding systems of the United States), the result 

 is precisely the same. The faunas of the consecutive systems differ 

 to the extent of the progress made in the locally unrepresented 

 interval ; and the group of rocks holding each fauna forms for the 

 geologist a convenient Procrustean bed to which to fit the tolerably 

 synchronous deposits of other lands. The unconformability argu- 

 ment is worthless except from the point of view that the faunas of 

 our typical British systems are likely to be the more distinct the 

 longer these separating interregnums lasted. It is best, that is, 

 simply as a matter of convenience and clearness of definition, to 



