556 S. a. Howorth — Traces of a Great Post- Glacial Flood. 



moderate temperature " (Trans. Geol. Soc. of G-lasgow, vol. ii. p. 51). 

 I am tempted to quote a passage, describing the condition of things 

 when life first crowded the previously glacial seas, from an observer 

 who did rare work as an explorer, namely, Dr. Eobert Brown, 

 Speaking of the clay now forming on the coasts of Greenland by 

 the deposit of its contents by the subglacial streams in the open sea, 

 he says, "In this clayey bed the arctic mollusca and other marine 

 animals find a congenial home, and burrow into it in great numbers. 

 However, as new deposits are thrown down, they keep near the 

 surface to be able to get their food " (Physics of Arctic Ice, by Brown, 

 Journ. Geol. Soc. vol. xxvi. pp. 682-3). 



The feature which specially characterizes the marine fauna of the 

 Polar Seas is the paucity of species which prevails there. Forbes 

 long ago pointed out " that a deficiency in species and individuals 

 of the testaceous forms of mollusca indicates, to the marine zoologist, 

 the probability of. a state of climate colder than that prevailing in 

 the same area at present." " Thus," he adds, " the existing fauna 

 of the Arctic Seas includes a much smaller number of testaceous 

 mollusca than those of the Mid-European seas, and the number of 

 testacea in the latter is much less than in the South-European and 

 Mediterranean regions. It is not the latitude but the temperature 

 which determines these differences " (Forbes, Mem. Geol. Survey, 

 vol. i. p. 367). There can be no doubt that the general evidence goes 

 to show that the marine climate was colder during the deposition of 

 the immediately Post-Glacial beds than it is now; but, as we shall 

 show presently, this has been much exaggerated and misunderstood. 



Everybody will admit that the Memoir just quoted was one of the 

 most remarkable and suggestive which was ever published, and that 

 it marks a great epoch in pal^ontological and biological generaliza- 

 tion. The greater portion of this Memoir, as is well known, is 

 taken up with an examination of the molluscan remains found 

 in the various drift deposits of the northern part of Great Britain, 

 which Forbes assigns to the Glacial epoch, speaking of the waters 

 in which they lived as the Glacial Sea, and of themselves as Glacial 

 Testacea. Forbes defines what he means very explicitly. He says : 

 " By Glacial epoch I intend to express that section of geological 

 time which was typically distinguished by the prevalence of severe 

 climatal conditions through a great part of the Northern hemisphere, 

 and during which those marine accumulations, in part truly sedi- 

 mentary deposits, which have been called Northern Drift, were 

 formed. I have selected the word ' Glacial ' in order to remind 

 geologists of the ice-charged condition of our seas during that epoch, 

 conditions which probably did not prevail during its earlier stage, 

 and the gradual disappearance of which marked its conclusion " 

 (op. cit. pp. 402 and 403). 



It is a bold thing to question the position of such a conchologist 

 as Edward Forbes, and it would be a practically hopeless one if he 

 and those who agreed with him did not virtually furnish us with 

 weapons out of their own mouths. The whole point that I wish 

 to raise is as to the connotation of the term Glacial as used by 



