go The I) isli Naturalists May, 



' It is with the last of these eight great trans-oceanic connections that 

 the student of Irish natural history will, as such, be chiefly concerned ; 

 but it would, of course, be unfair to Dr. ScharfE to treat his arguments 

 on that subject as the main feature of his book, in which so man}^ questions 

 of extraordinary difficulty and complexity have been handled with even 

 greater skill and force of argument than the author has shown in his 

 previous books. In intimate connection with Dr. Scharff's view of a 

 late Pliocene connection between Labrador and western Europe must be 

 taken his view of the nature and cause of the Ice Age, on which, discuss 

 it as we may, agreement does not seem likely to be arrived at for a long 

 time. In North America, as in Ireland, Dr. Scharft" holds that the Ice 

 Age cannot have been an exterminating factor, since a considerable 

 number of species existed both before and after it in Greenland and other 

 glaciated areas which have not been found fossil outside those areas. 

 Dr. Scharff strongly inclines to the view that the Ice Age was actually 

 caused by a simultaneous closing of the Arctic Ocean to the waters of 

 both the Atlantic and Pacific, which would have the double effect of 

 reducing the temperature north of the barrier and raising it in the regions 

 immediately south of it. Thus he holds that parts of Greenland and 

 Alaska enjoyed quite a comfortable climate during the Ice Age, and were 

 able in consequence to support a much richer fauna and flora than would 

 be possible in either of those countries at the present time. 



It may be worth asking here whether Dr. Scharff's argument does not 

 tend to prove rather too much. If the ocean expanse between Europe 

 and North America was bridged during Pleistocene times, and 

 the bridge was broken not long before the commencement of the 

 the Glacial Period, the final severance between Europe and North America 

 was not geologically much more remote — if at all so — than (according 

 to Dr. Scharff's elsewhere expressed views) the severance between Great 

 Britain and Ireland. Ought not the west European and North American 

 faunas to be, on that hypothesis, much more closely akin than they actually 

 are ? Dr. Scharff repudiates the idea of a merely discontinuous con- 

 nection, through an intervening land that may at one time have touched 

 America on the west, and at another time Europe on the east ; arguing 

 that if that were so the transmissions should all have been in one direction, 

 whereas he finds that each of the two continents has sent species to the 

 other. The same bridge that brought the Reindeer — possibly also the 

 Musk Ox — and a few such plants as Naias flexilis and Spiranthes roman- 

 zoviana eastward from America to the British Islands was likewise used 

 by the running beetle Carabus catenulatiis and the snail Helix hortensis to 

 extend their ranges westward into America. Therefore the way was open 

 for a hither -and -thither intermigration between the two continents, and 

 the puzzle is why was the interchange not more general ? Dr. Scharff 

 suggests (p. 25) that part of the bridge was obstructed by glaciers as 

 soon as the Ice Age began. The animals that got over were, in fact, 

 the race -winners, and it is highly , creditable to Helix hortensis to have 

 been among the successful few ! 



