Feb. 24, 1 881] 



NA TURE 



593 



operation whereby the British IslaiuU were isolated. We these is discussed the important question of the origin of 

 must not forget however that denudation also played its the European element in the floras of the temperate 

 part. The eNcavation of the Strait of Dover, for example, southern latitudes. 



may have been in large measure effected by streams Enough has been said here to show the nature and 

 diverging from the watershed and partly by the littoral value of this new contribution to scientific literature, 

 erosion of the waves as they advanced upon the slowly ' Even where Mr. Wallace's conclusions may be disputed, 

 foundering land. The recent date of the separation of | they are always of the most suggestive kind. His volume, 

 Britain is shown by the identity of the fauna as a whole with , as he acluiowledges, is the development and application of 

 that of France and Germany. But as compared with the a theory; but it is not written in the spirit of a mere 

 continent, the British Isles are remarkably poor in species. , partisan. Its facts are of course marshalled in such form 

 In Germany, for example, tliere are nearly ninety species ' as most effectively to sustain the theory; yet with a trans- 

 of land mammals ; even Scandinavia possesses about I parent directness and honesty of purpose that runs 

 sixty ; but Britain can boast only forty- a number which \ through the whole book, and gives it one of its great 

 in Ireland is reduced to twenty-two. Still more remarkable j charms. The writer does not consciously shut his eyes to 

 is the contrast presented by the reptiles and amphibia ; 1 any of the difficulties of his case. Candidly admitting 

 for while Belgium possesses twenty-two species, Britain ' them, he presents such explanation as seems to him to 

 can show no more than thirteen, and Ireland has only ' offer the most likely pathway to their ultimate solution, 

 four. This progressive diminution of the fauna 



westward is even illustrated by animals possessing 

 the power of flight, though, as might be supposed, 

 it is in these cases less strongly marked. The 

 twelve bats of Britain are reduced to seven in 

 Ireland, the 130 land-birds to about no. In 

 Britain 1425 species of flowering plants and ferns 

 are known, but in Ireland only 970, or two-thirds 

 of the British flora. The reason assigned by Mr. 

 Wallace for this poverty of species is the exten- i 

 sive submergence of the British Islands during ■ 

 the later stages of the Glacial Period. He be- 

 lieves that the interval between the subsequent 

 elevation and the final separation of Britain from 

 the continent cannot have been of long duration. 

 It was indeed sufficiently prolonged to allow of 

 the migration westwards of a considerable part 

 of tlie Post-glacial fauna and flora, but the insular 

 condition was established before more than a 

 part had succeeded in reaching Britain, where 

 both the soil and climate would have been 

 eminently favourable for the reception of the rest. 

 The time that has elapsed since our area cea - ' 

 to be continental has been long enough for li 

 production of a few peculiar varieties. No dio- 

 tinct species or variety of mammal, reptile, or 

 amphibian has arisen. But we possess three 

 peculiar birds — the coal-tit, long-tailed tit, and 

 grouse — fifteen peculiar species of fresh-water 

 fishes, sixty-nine lepidopterous insects, seventy-two 

 beetles, four caddis-flies, and four terrestrial and 

 fluviatile shells belifved to be peculiar. In the 

 flora the chief < ontrasts are exhibited by the 

 mosses and hepatics, of which respectively seven- 

 teen and nine forms appear to be peculiar. This 

 mode of considering the British fauna and flora j 

 brings out in clear relief the relations between 

 them and those of the continent, and their bear- 

 ings upon the question of the origin of peculiar 

 forms. Not only do the British Islands as a whole Fig. 2.— Map 

 contain species or varieties that do not appear 

 on the mainland of Europe, but some of our outlying 

 islands, such as the Shetland Isles, the Isle of 

 Man, and Lundy Island, possess each its local forms 

 that are not met with on the main island. 



As "anomalous islands" the author classes together 

 Celebes and New Zealand, the former because it belongs 

 to no one of the six zoological regions of the globe, and 

 cannot be certainly affirmed to have been united to a 

 continent, the latter because in some respects it may be 

 regarded as an oceanic, in others as a continental island. 

 Celebes is supposed by Mr. Wallace to be probably a 

 fragment of Miocene Asia, preserving down to the present 

 time a few remnants of its Tertiary fauna, together with 

 an intermixture of more modern types that have been 

 introduced by ordinary means of dispersal. Three 



in depth. The figures 

 Norway and Denmark 



1 bank connecting the British Isles with the Continent. The 

 nore than, the paler tint shows sea of 'ess than, looo fathoms 

 show the depth in fathoms. The narrow channel between 

 is 2580 feet deep. 



interesting chapters are devoted to New Zealand, and in 



He deserves the thanks alike of geologists and of biologists 

 for a treatise, the appearance of which marks another 

 epoch in the history of the doctrine of Evolution. 



Arch. Geikie 



HONOUR TO MR. DARWIN 



THE following address to Mr. Darwin, from New 

 Zealand, speaks for itself : — 



To Charles Darwin, Esq. 

 Sir,— We, the members of the Council of the Otago 



Institute, beg to offer you our congratulations on this, the 



