410 JOURNAL OF SCIENCE. 
but he does not bring forward a particle of evidence in support 
of his opinion, and indeed it would be impossible to do so as we 
cannot examine any sections through these plateaux. More- 
over there is no reason to suppose that volcanic agencies upheave 
the sea bottom any more than they do the land. Massive 
eruptions, which Dr. A. Geikie allows to have been submarine, 
break through the superincumbent rocks exactly as does the 
pipe of a volcano. 
Dr. Carpenter also insists upon the persistence of cretaceous 
types of animals in the Atlantic up to the present day as proving 
that the North Atlantic has not been land since the termination 
of the cretaceous period. There is, no doubt, much force in this 
argument ; but it is not conclusive, for the deep sea fauna is much 
the same all over the world, and if the bed of the North Atlantic 
had sunk at a comparatively late period it would probably have 
been invaded by the fauna of the South Atlantic, which closely 
resembles it. 
I do not attach much weight to the argument that the direc- 
tions of first relief of pressure caused by a shrinking nucleus 
under a rigid earth crust must always afterwards remain the 
direction of further relief, because we really know so little of the 
conditions of the problem. It looks plausible, but we must 
remember that great subsidences have certainly taken place in 
former areas of elevation which, by hypothesis, were areas of 
relief; and we should expect that the areas of relief would be 
far more numerous than the three great meridional lines of eleva- 
tion. Weknow, asa matter of fact, that continental areas are 
liable to subsidence, and that oceanic areas are liable to eleva- 
tion; and we cannot as yet place a limit on the possible 
amount of continental depression or of oceanic elevation. 
Mr. Wallace’s argument that rocks of all ages, on all conti- 
nents, contain the remains of land, or fresh-water, or estuarine 
animals, or of plants, is of no special value, because it is only a 
restatement of the argument that all the sedimentary rocks are 
shallow water deposits, which is admitted. If we were to finda 
complete, or nearly complete, series of rocks from some ancient 
date up to the present day represented in a continental area, 
then that continental area must have been permanent since that 
ancient date, but this is never the case. We certainly do find a 
large number of geological periods represented in Europe, Asia, 
America, Australia, and New Zealand, but in all cases there are 
also long periods unrepresented, especially in the Paleozoic era, 
where there are many physical breaksin continuity, accompanied 
by an almost complete change in animal life, and Sir A. Ram- 
say says that these breaks may each indicate a period of time as 
ereat as the vast accumulations of the whole Silurian series. The 
question is, what was the condition of these areas during the un- 
represented periods? Certainly they might have been land, but 
also they might, in some cases at least, have been deep ocean. 
Our knowledge of the geology of the world is, at present, quite 
insufficient to settle this question. 
