6 G. F. MATTHEW ON THE 



lu the comparison of species it is found that the resemblance between the Cambrian 

 faunas of the two sides of the Atlantic Ocean is very close. This resemblance is not con- 

 fined to the Paradoxides fauna, but extends to the later faunas as well ; for in the Peltura 

 fauna a number of trilobites occur in Eastern Canada which are either varieties of Euro- 

 pean species, or are closely related representative species. And the same rule holds as 

 regards the trilobites of the next fauna (Arenig horizon) in so far as the imperfect material 

 known, admits of comparison. 



How widely contrasted in genera, as well as in species, were the faunas of theinterior 

 of America from those of the Atlantic coast throughout the Cambrian age. Even though 

 we should eliminate the synonyms which at present make the differences seem greater 

 than they actiially are. sufficient divergence remains to show how widely contrasted were 

 the conditions of life in these two regions. And further, we note that these diverse con- 

 ditions not only affected wide areas of the earth's surface, but were of long continuance, 

 for they included a large part of early Palaeozoic time. 



III. — Physical Conditions affecting the Distribution of the Faunas. 



The peculiar regional diversity of the Cambrian faunas in these contiguous regions 

 of America it seems to the author is most readily explicable in the view that areas of sea- 

 water of different temperatures existed in these two regions during the whole of the 

 Cambrian age, and that this served to establish and perpetuate the distinction of faunas. 



A polar current from the north of Europe to America, if once established, would tend 

 to perpetuate itself It would be confirmed in its course and its channel deepened owing 

 to the sinkiuff of the earth's crust beneath it, due to the convection of heat from the 

 earth's interior by the cold waters of the current, condensing and hardening the solid 

 matter beneath. The yielding and expanding of the crust would be in regions outside ot 

 the influence of the current, and might produce such mountain ranges as are now found 

 bordering the Atlantic shore of America. Such in outline might have been the history 

 of the physical features impressed upon the earth's surface in this region in Cambrian 

 times or earlier, as held by Dana and others who have given attention to the origin of the 

 continents and oceans. 



A polar current such as we have described could not have existed without a corres- 

 ponding flow of tepid waters from the equatorial regions to the poles. A passage for 

 such waters to the Arctic regions across the central part of North America seems to be 

 indicated by the occurrence of molluscan remains of Chazy types in the polar regions, 

 and at intervals along the western border of the Laurentian area of Canada from the 

 Ottawa River to Boothia. Such traces of the latest Cambrian fauna' do not end here, but 

 continue onward to the north of Greenland, whence the passage is short to the north of 

 Europe, where Chazy forms reappear. The sketch-map at page 13 of this paper will 

 show the contrasted range of the Cah'iferous-Chazy and the Arenig faunas. 



Dana in his Manual of Geology develops at considerable length a theory of the 

 antiqixity of the continents and the permanency of the ocean basins, and he, as well as 

 other observers, has attributed the ridging up of the continental borders to the lateral 



' The Calciferoua faunas, many of whose forms continue on in the Chazy- 



