56 OiN mm LAND AND FRESH-WATER 



prepared catalogues illustrative of the zoology and botany of the 

 interior of Canada. From Mr. Bell, and from other observers we 

 learn that many of our common fresh-water shells occur in post- 

 pliocene beds of much higher antiquity than our lacustrine marls, 

 while one, if not two, of our Lower Canadian land snails, is of as 

 high an antiquity as the Upper Eocene formation. The Helix 

 labyrinthica of Say, a little snail not uncommon in a living 

 state in Canada, has been found fossil in the Upper Eocene lime- 

 stones of Headon Hill in the Isle of Wight, and also in the Paris 

 basin. It has been suggested too, that the Helix omphalos, of 

 Searles Wood, another of the Headon Hill fossils, is identical 

 with a living Canadian snail, the Helix striatella of Anthony. 



The late lamented Edward Forbes has shown us the importance 

 of studying the fossils of the newer tertiaries in connection with the 

 distribution of living animals and plants. It appears to me to be 

 well, in order clearly to understand our subject, briefly to epito- 

 mize, as on a former occasion, his brilliant and most profoundly 

 philosophical generalizations. On the tops of the mountains near 

 the lakes of Killarney, in Ireland, occur a few plants, entirely 

 different from those of the mountains of North Wales and Scotland, 

 but nearly agreeing with those of the Asturian mountains in the 

 north of Spain. According to Forbes, the southern character of 

 these few plants, and their extreme isolation, (together with col- 

 lateral facts respecting the peculiar distribution of the marine in- 

 vertebrata of that region) point to a period when a great moun- 

 tain barrier extended across part of the Atlantic, uniting Ireland 

 with Spain. Soon after this, arguing from similar data, he infers 

 that another barrier of high land connected the west of France 

 with the southwest of England, and thence with Ireland : while a 

 little later England and France were connected by dry land towards 

 the eastern end of the English Channel. As tending to prove this 

 latter view, we may cite the fact, well known to European geolo- 

 gists, that one fresh-water and one land snail, (Bithinia marginata, 

 and Helix incarnata) abundant as post-pliocene fossils in the valley 

 of the Thames, are still living in France, though extinct in Great 

 Britain. At the time of the glacial drift, what are now the 

 summits of the Scotch and Welsh mountains, were then, Forbes 

 argues, low islands, or members of chains of islands, extending 

 to the area of Norway, through a glacial sea, and clothed with an 

 Arctic vegetation, which in the gradual upheaval of those moun- 

 tains, and consequent change of climate, became limited to the 



