1922 CHRONOLOGY 23 



to point to such modem cases, it would be necessar\% if the parallehsm 

 is to be exact, to show that the modem rivers were of the same class 

 as the Jurassic streams — consequents and consequents must be paraUeled, 

 not subsequents with consequents. 



Thus the enquiry branches out far beyond the limits of a work 

 on Ammonites. And it is easy to see that in other directions evidence 

 is to be sought. For, if the estuarine beds belong to different river- 

 systems, opening into different oceans, their faunal contents should 

 reveal such facts. But this is not a line of Ammonite enquiry. 



Pause may be made here to indicate something of interest : 

 that the nearest modem geographical parallel to the Jureuropean Sea 

 and its bordering lands is to be found in the Arctic Ocean and surrounding 

 continents. This is noticeable, because there America comes into nearest 

 contact \rith Europe. According to Dr. Wegener's theor\' of drifting 

 continents, America was in close proximity to Europe a few million 

 years ago — a period of time less than may be supposed to have elapsed 

 since the close of the Jurassic Period. But, if America was not far distant 

 from Juroceltia in the Jurassic Period, faunal and stratal similarity' in 

 the American and European Jurassic deposits should be expected. 

 On such subject the value of very detailed chronological analyses \v\]l 

 be shown : for, if there be such similarity, it would be evidence in favour 

 of the theory, though if there be not, it would not be fatal to it. Between 

 the Ammonite-fauna of Jureuropea and that of the west coast of South 

 America there is very considerable similarity — the connexion is supposed 

 to have been made by an extension of the Jureuropean sea, Tethys, 

 as a mediterranean between the north shore of Gondwanaland and the 

 south shore of Atlantis. But there is little, if any, similarity between 

 the Ammonite-faunas of Jureuropea and North America. Whether 

 America was close to Europe or was in its present position makes no 

 essential difference to the geography of the Jurassic — in the first place 

 Tethys would be depicted in length as great as the present Atlantic, 

 in the second, it would be shown as very short. Except for such 

 difference in length, the general configuration of land and water would 

 be similar. In \ridth, Tethys, as an open sea Ipng to the west of the 

 island of Juroceltia, may be postulated as stretching from Rockall 

 to Madeira. 



Returning now to the Arctic Ocean — this is a sea almost surrounded 

 by land. If Davis Strait and the Greenland Sea be imagined as closed 

 by land, then there is a geographical parallel to the Jureuropean Sea 

 in earliest Caloceratan Age. The breaking dowTi of these barriers — 

 the Greenland Sea corresponding to the Biscayan gateway and Davis 

 Strait to the Hebridean gateway — makes a geographical parallel to the 

 Jureuropean sea — and land — conditions during the rest of the Ammoni- 

 toidic Period. The Bering-Straits outlet corresponds to the outlet in 

 South-East Europe, which was presumably closed when the western 

 gateways were opened. If the Arctic-Ocean area be turned through 

 90 degrees to the east, so that Greenland Hes to the west, and Bering 

 Straits to the east, the parallelism with Jureuropea is ver\^ close. 



As regards islands, Greenland then corresponds to Juroceltia, while 

 the various archipelagos dotted about the Arctic Ocean parallel various 

 similar fieatures which may be postulated for Jureuropea. Earth- 

 movements connecting these islands or other land-areas together would 

 make temporary faunal provinces, distinguished by faunal dissimilarity. 

 And dependent on such crustal movements must be raising of certain 



