GEOGRAPHICAL BISTfilBUTION — PAST AND PEESENI. 215 



83° 43'. These species, moreover, appear to have been just as 

 abundant in their respective positions north of the Arctic circle as 

 they were south of it. The coz'al fauna of the same region com- 

 prises, among other forms common to both Europe and North 

 America, such wide-spread species as Favosites Gothlandica and 

 Halysites catenulata, both from latitude 79° 45' (Cape Frtteer) ; 

 Lithostrotion junceum has been found as far north as latitude 8^° 

 43' (Fieldeu Isthmus). 



Turning our attention to a somewhat antipodal portion of the 

 earth's surface, Australia, we find that by far the greater number 

 of fossils that have been catalogued from its Paleozoic deposits are 

 species that were originally described from regions lying well with- 

 in the limits of the north Temperate Zone. In fact, the relationship 

 existing between this southern fauna and the faunas of Europe and 

 North America is so great as to practically amount to identity. 

 This correspondence is perhaps as well exhibited by the graptolites 

 as by any other group of animals, for we find that of the twenty- 

 fom- species recorded by Mr. Robert Etheridge, Jr., in his "Cata- 

 logue of Australian Fossils " (1878), no less than eighteen are 

 species belonging to the United States and Canada. When we 

 seek to explain the broad distribution of life in the early periods of 

 the earth's history compared to what it is at the present time, it 

 will naturally be concluded that greater facilities for dispersion, and 

 the prevalence of more equable conditions of climate, especially the 

 latter, were the prime factors involved in this distribution. If, as 

 may be contended, other conditions were also largely instrumental in 

 bringing about the general result, we are entirely ignorant of their 

 nature. That a different disposition of the land and water areas 

 than now obtains may have facilitated distribution in a manner 

 now no longer possible must be conceded, and there are abundant 

 proofs that considerable alterations of one kind or another, whether 

 in favour of, or against, dispersion, have at various times taken 

 place. But it is beyond question, as is shown by the distribution 

 of our existing marine fauna, that while the relations existing be- 

 tween land and water have much to do with distribution, yet the 

 determining factor in such distribution is after all the matter of 

 temperature. The comparatively limited north and south extent 

 of any fauna, even along a continuous coast line, contrasted with 

 its broad east and west range, sufficiently proves this to be the 



