H. H. Howorth—Traces of a Great Post-Glacial Flood. 9 
It is also evident that in Scotland the largest number of species 
have been obtained from the Llandeilo; of these about 22 are com- 
mon to the Caradoc, 7 pass into the Llandovery, 3 into the Wenlock, 
and 1 into the Ludlow. 
Of the Caradoc species 11 pass into the Llandovery (chiefly the 
Lower Llandovery), 17 from the Llandovery (chiefly Middle and 
Upper Llandovery) into the Wenlock and Ludlow. 
It is also evident from these approximate and provisional estimates, 
that in Scotland the larger number of species are restricted to their 
formation. The Llandeilo is extremely rich, and although only 
about a third of its species are found in the Caradoc of Scotland, 
some more of them occur in the Caradoc of England, but the exact 
line of separation between the Lower Caradoc and Upper Llandeilo 
has still to be correctly defined, as also the different horizons of the 
Llandeilo itself. 
I have followed in my table the classification of the Silurian rocks 
of Scotland as recently proposed by Prof. C. Lapworth, F.G.S. 
More collecting and further study of the species will no doubt 
tend to modify the numbers we have given, and which are pro- 
visional and the result of our personal investigation. The larger 
portion of my material with respect to Scottish Silurian Brachiopoda 
has been contributed by Mrs. R. Gray, and by the Director-General 
of the Survey of Great Britain, or Museum of the Geological Survey 
of Scotland. The Pentland Hill series was kindly sent to me by 
Mr. J. Haswell, Mr. J Henderson, and Mr. D. J. Brown. 
Il].—Traces or a Great Post-GuactaL FuLoop. 
}. EVIDENCE oF THE Marine Drirt. 
By Henry H. Howortn, F-.S.A. 
(Continued from Decade II. Vol. IX. 1882, p. 559.) 
NOTHER series of beds, comprising those which are raised a 
considerable height above the sea, contain a congeries of mixed 
shells, often broken, and clearly, as we shall show presently, 
not in siti ; sometimes the shells are imbedded in sand and some- 
times in clay. They contain generally a larger proportion of species, 
and belong to a more temperate condition of things. The fact that 
Arctic shells are found in these higher beds is undoubted ; but, as I 
contend, the meaning of this is very different to what is often sup- 
posed,—the proportion of purely Arctic shells being by no means 
large, and under any circumstances the mollusca clearly pointing to 
a condition of things very different indeed to that which must have — 
existed when the great boulder heaps of Smaland and Finland, 
which I have travelled across for scores of miles with amazement. 
were being fashioned,—when our azoic Boulder-clays were being 
manufactured, and when the mollusca which prevail in high latitudes 
were driven far to the south, to the Mediterranean and elsewhere, 
where a few of their descendants are still found in very deep water 
and sporadically. During the Glacial period proper it is exceedingly 
probable that the sea was in fact as denuded of life as the land is. 
