432 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



cific time — the author himself so states — the priority apparently belongs 

 to Dana. 



In the second (1874) and third (1880) editions of his Manual, Dana's 

 three maps of 1863 remained practically unchanged, but in the fourth edi- 

 tion (1895) six new and much improved maps are presented. An analysis 

 of these shows that they are not based on a limited time, but are com- 

 posite maps of an entire system; further, that the seas are made to 

 spread over vast portions of the North American continent, where no 

 rocks of the system under consideration are known even at the present 

 day. This idea of "universal oceans" is forcibly brought to one's atten- 

 tion in Dana's map of the Siluric — a time, as will be shown later, when 

 not only vast areas of the continent were above the sea, but during 

 which there was also an irregularly progressive submergence followed by 

 a widespread elevation. Moreover, these maps do not take into account 

 the various and distinct contemporaneous faunas, each of which is re- 

 stricted to a limited region. If, as depicted by Dana, the broad Siluric 

 ocean is to be accepted without intermediate land barriers, these faunas 

 should then have a universal expression, which, as paleontologists know, is 

 not the case. However, Dana's maps bring out clearly his widely known 

 hypothesis of the gradual emergence of the North American continent 

 and the progressive accretion of younger and younger deposits around his 

 great Laurentian V — the nucleus of North America. Only in the most 

 general way can agreement be had with this hypothesis, for it will be seen 

 that the sea transgresses often and widely over the earlier accretions to 

 the North American nucleus. 



In 1883 the Austrian philosophical paleontologist Neurnayr published 

 his celebrated paper "Ueber Klimatische Zonen wahrend der Jura und 

 Kreidezeit," which includes what is probably the first paleogeographic 

 map of the world. Here, again, no definite time is represented, the map 

 being a composite picture of all the Jurassic. After more than thirteen 

 years of study on the Jurassic ammonites, Neumayr here announced the 

 distinct principle of localized and widely distributed marine faunas that 

 appear to be arranged in liomoiozoic or parallel belts due probably to zones 

 of different temperature. On the basis of this distribution of marine 

 Jurassic fossils he conceived the great transverse continent of Gondwana — 

 a continent that has since become reduced to the present India, Africa, 

 and South America. He likewise was the first to point out the fact that 

 in all probability during Jurassic time there were climatic or temperature 

 zones very similar in position to the temperate and tropical belts of today, 

 yet no Permic nor Cambric tillites and scratched grounds had then been 

 discovered. 



