^ ADDRESS. 33 



animal and vegetable colonists for longer periods, go far to show that, 

 time being given, the sea actually affords facilities for the migration of the 

 inhabitants of the land, comparable with those of continuous continents. 



In so far as plants are concerned, it is to be observed that the early 

 forests were largely composed of cryptogamous plants, and the spores of 

 these in modern times have proved capable of transmission for great 

 distances. In considering this we cannot fail to conclude that the union of 

 simple cryptogamous fructification with arboreal stems of high complexity, 

 so well illustrated by Dr. Williamson, had a direct relation to the neces- 

 sity for a rapid and wide distribution of these ancient trees. It seems 

 also certain that some spores, as, for example, those of the Rhizocarps,' 

 a type of vegetation abundant in the Palaeozoic, and certain kinds of 

 seeds, as those named ^theotesta and PacJnjtheca, were fitted for flotation. 

 Farther, the periods of Arctic warmth permitted the passage around the 

 northern belt of many temperate species of plants, just as now happens 

 with the Arctic flora; and when these were dispersed by colder periods they 

 marched southward along both sides of the sea on the mountain chains. 



The same remark applies to northern forms of marine invertebrates, 

 which are much more widely distributed in longitude than those farther 

 south. The late Mr. Gwyn Jeffreys, in one of his latest communications 

 to this Association, stated that 54 per cent, of the shallow-water 

 mollusks of New England and Canada are also European, and of the 

 deep-sea forms 30 out of 35 ; these last of course enjoying greater 

 facilities for migration than those which have to travel slowly along the 

 shallows of the coasts in order to cross the ocean and settle themselves 

 on both sides. Many of these animals, like the common mussel and 

 sand-clam, are old settlers which came over in the Pleistocene period, 

 or even earlier. Others, like the common periwinkle, seem to have been 

 slowly extending themselves in modern times, perhaps even by the agency 

 of man. The older immigrants may possibly have taken advantage of lines 

 of coast now submerged, or of warm periods, when they could creep 

 around by the Arctic shores. Mr. Herbert Carpenter and other natu- 

 ralists employed on the Challenger collections have made similar state- 

 ments respecting other marine invertebrates, as, for instance, the Bchino- 

 derms, of which the deep-sea crinoids present many common species, 

 and my own collections prove that many of the shallow-water forms are 

 common. Dall and Whiteaves- have shown that some mollusks and 

 Echinoderms are common even to the Atlantic and Pacific coasts of 

 North America ; a remarkable fact, testifying at once to the fixity of these 

 species and to the manner in which they have been able to take advantage 

 of geographical changes. Some of the species of whelks common to the 



Si>ecial Memoirs on the Brachiojiods, Cephalopods, S,-c.\ and B.a].\, Palceontology of 

 New York ; Billings, Reports on Canadian Fossils ; and Matthews, Cambrian of New 

 Brunswich, Trans. R.S.C. 



' See paper by the author on Palaozoic Khizocarps, Chicago Trans. 1886. 



- Dall, Report on Alaska; Whiteaves, Trans. R.S.C. 

 1886. P 



