PAL^OGEOGRAPHIC MAPS 1145 



in 1856, by B. Crivelli for Italy in 1853 and by Gemmellaro for 

 Sicily in 1834. (Dacque-i2:/pi'.) The most elaborate recent at- 

 tempt to map the conditions of land and water at different geologic 

 periods is that of Schuchert, who, in his instructive monograph on 

 the Palgeogeography of North America, has published fifty separate 

 maps showing the changes in outlines of North America from 

 Cambric to Pliocenic time. 



Types of Pal.eogeographic Maps. Palseogeographic maps may 

 be simple or complex, special or generalized. The simple map aims 

 to show the distribution of geographic features, of a particular pe- 

 riod in the earth's history, over the surface of the earth, much as a 

 modern geographic map shows this distribution for the present time ; 

 a complex map, on the other hand, attempts to show more than this. 

 The simple map need not be confined to the depiction of the hypo- 

 thetical coastline, but, if the facts available allow it, should repre- 

 sent the ocean currents, the mountains, the rivers, etc. As examples 

 of maps of this type, though very incomplete, especially in so far as 

 the land features are concerned, may be mentioned the Ordovicic 

 map by Ruedemann (38) and those for the same time-period by 

 Grabau (18); the older Devonic maps. of Schuchert, and many 

 others. The excellent maps by De Lapparent (31) may ^Iso be 

 classed here, though on them the areas of continental as well as 

 marine sedimentation are shown. The complex maps may show, 

 in addition to the deduced geographic conditions, some of the data 

 on which this deduction is based, especially the distribution of the 

 geological formation in question, or of its outcrops. Such a map 

 is in reality a combination of a paLneogeographic and a geologic 

 map, and this may prove highly useful, for the degree of detail de- 

 picted upon the map, and the extent to which the map is hypotheti- 

 cal, are at once apparent. Such are the maps issued by Schuchert 

 for North America. A somewhat more complicated type is repre- 

 sented by the Pal?eogeographic maps issued by Chamberlin and 

 Salisbury (10) where the attempt is made to represent not only the 

 outcrop, but also the parts believed to exist beneath cover, and 

 the areas from which the formations are believed to be removed 

 by erosion. 



The most complex and detailed maps of this type published in 

 America are those issued by Bailey Willis (57; 59). In them the 

 attempt is made to represent the oceanic basins, the littoral and the 

 epicontinental waters, the areas which may have been either sea 

 or land — separating those which were more likely sea and those 

 which were more likely land — the lands of the time, the indetermi- 

 nate areas, and the ocean currents, both polar and equatorial. 



