680 JAMES PERRIN SMITH 



from the outside world. The appearance of such genera or spe- 

 cies is an interregional event, and marks an episode in the 

 dynamic history of the earth. Zones are thus not a figment of 

 the stratigrapher's imagination, but are based on geologic events 

 of far-reaching importance, in comparison with which the local 

 shiftings of lithologic facies are insignificant. 



Ancie?it fau?ial geography. — One of the first things that 

 attracted the attention of naturalists engaged in the study of 

 geographic zoology was that animals are not now distributed 

 strictly according to climate, or other physical conditions. 

 Edward Forbes early reached the conclusion that the ancient 

 marine faunal provinces and regions by no means corresponded 

 with the present distribution, and that the present faunal rela- 

 tions could be explained only by study of past geologic changes 

 in the distribution of land and water. The various marine prov- 

 inces were grouped by S. P. Woodward 1 in great regions : "The 

 tropical and subtropical provinces might naturally be grouped 

 in three principal divisions, viz., the Atlantic, the Indo-Pacific, 

 and the West-American — divisions which are bounded by merid- 

 ians of longitude, not parallels of latitude. The Arctic prov- 

 ince is comparatively small and exceptional; and the three 

 most southern faunas of America, Africa, and Australia differ 

 extremly, but not on account of climate." 



What is true of faunal geography today was true of it in the 

 past. While certain faunas, such as the Silurian, have been very 

 widely distributed, on account of the existence then of wide 

 expanses of shallow marginal and epicontinental seas, there were 

 no such things as universal faunas, even in the most remote 

 geologic time. There have always been barriers of continent 

 and ocean, and probably too of climate, ever since life existed 

 on the earth. Only the deep sea faunas could be universal if 

 oceanic basins had been stable; but such faunas are not uni- 

 versal now, nor have they remained unchanged in time. 



Many years ago Barrande 2 showed that the Cambrian 



'Manual of the Mollusca, 1856, p. 353. 



2 Systeme Siluiien du Centre de la Boheme. 



