388 SCIEXCE PROGRESS. 



supply of oxygen, and life m the deep sea became possible 

 for the first time. There have been many speculations as 

 to how a nearly uniform temperature could have been 

 brought about in sea-water over the whole surface of the 

 earth in early geological ages, as well as to how sufficient 

 light could have been present at the poles to permit of the 

 luxuriant vegetation that once flourished in these regions. 

 The explanation that appears to me the most satisfactory is 

 the one which attributes these conditions to the very much 

 greater size of the sun in the early stages of the earth's 

 history — an idea first introduced into geological speculations 

 by Blandet, who likewise discussed the relations of Arctic 

 and Antarctic faunas — together with the greater amount of 

 aqueous vapour in the atmosphere, and the greater mass of 

 the atmosphere." The pelagic Algae, Radiolaria and Fora- 

 minifera, he holds, are probably the but slightly modified 

 descendants of a very ancient universal pelagic fauna and 

 flora, and life in its simplest form most likely first appeared 

 in Pre-Cambrian times in the detrital matters laid down 

 about the mud-line, when the mud-line was not so deep, and 

 the land surfaces were more extensive than at the present 

 time. These speculations are not stated without a gallant 

 array of facts, and if the style of their exposition be some- 

 what insistent it is inspired by the fire of enthusiasm. The 

 theorv is comforting- to the naturalist. Criticism must come 

 from the student of solar physics and from the geologist. 

 It may quite possibly prove that the Arctic fossil coral reefs 

 are mostly, if not all of them, Bryozoa reefs — the point 

 needs further research — and it may be that botanists have 

 accepted on evidence that is not quite so convincing as was 

 formerly supposed Heer's contention that Greenland once 

 had a warm climate, — in short the provocation for Dr. 

 Murray's theory may be less slender, but it is hard in any 

 case to get over the evidence of massive calcium carbonate 

 organic deposits in ancient Arctic seas always associated 

 with warm waters, or the occurrence of veritable fossil tree- 

 ferns like Dicksonia in Greenland. 



Appended to the second part are two belated special 

 memoirs, that on Spirula by the late Mr. Huxley and Dr. 



