16 Proceedings of the Royal Physical Society. 
over, unless the circumstances conducing to its preservation 
were exceptionally favourable, we could not expect to find 
a deep-sea deposit in the present dry land occupying more 
than a very limited area. 
The above reasons render it certain that any record that 
we may have of the deep-sea deposits of past geological ages 
in our present lands must be of an extremely fragmentary 
description. Nevertheless, recent researches have shown 
that the argument in favour of the permanence of the deep 
ocean-basins, founded upon the supposed absence in the 
dry lands of any deposits comparable with the modern deep- 
sea muds, is not supported by the actual facts of the case. 
On the contrary, we know now of a considerable number 
of stratified deposits—varying in age from the Ordovician, 
or perhaps some still older period, to the late Tertiary— 
which may, with more or less of certainty, be regarded as 
of deep-water origin; and these bulk as largely in the 
geological series’as, from their mode of formation, they could 
reasonably be expected to do. 
For my present purpose it will be sufficient to restrict my 
remarks on this point principally to those deposits in the 
dry lands which admit of comparison with the Radiolarian 
ooze of the modern deep seas. ‘The occurrence of fossil 
Radiolarians in late Tertiary deposits, such as the “ Barbados 
Earth,” has been known since the time of Ehrenberg. At 
a later period, the presence of Radiolarians in rocks of 
Cretaceous age was shown by Zittel (Zeitschr. d. deutsch. Geol. 
Gesell., 1876); and Dunikowski demonstrated the existence 
of organisms belonging to the same group in the Lower 
Lias of Germany (Denkschr. d. k. Akad. d. Wiss. Wien, 1882). 
It is, however, essentially to Riist that we owe the discovery 
that various jaspers, cherts, and other siliceous rocks of 
different geological ages are truly of the nature of fossil 
Radiolarian oozes. This was fully established by Riist in 
his “Memoir on Jurassic Radiolarians” (Palwontographica, 
1885); and the same observer also recognised the occurrence 
of similar Radiolarian deposits in rocks of Paleozoic age, 
though I am not aware that his researches on this subject 
have yet been published. The first observer, however, to 
