92 J. Barrett — Upper Devonian Delta of the 



is here excluded, and the present map rests in part upon publi- 

 cations by the United States and New York Surveys issued 

 since the map by Willis was published. A large difference is, 

 however, owing to another cause. In Lycoming County, in 

 North Central Pennsylvania, Willis takes data from Andrew 

 Sherwood* for the thicknesses of the Upper Devonian. But 

 these are measurements of partial and not complete sections. 

 Their use gave an apparent lack of sedimentation and conse- 

 quent constriction of the geosyncline. The present map in 

 that region has been controlled by the very complete section 

 measured by H. M. Chance. f But it is in the location of the 

 margins of the basin that the two maps differ most widely ; 

 the differences being the result of the application of different 

 principles for the location of the original margins of eroded 

 formations. Willis has crystallized these more definitely and 

 consciously than others of the living geologists and their dis- 

 cussion is taken up in detail in later sections of this article. 

 The two maps are important in showing the wide difference in 

 results which may flow from different interpretations of the 

 same set of facts. 



In 1906 Chamberlin and Salisbury published a set of paleo- 

 geographic maps which showed distinct advances over those 

 preceding.;}: The map for the Upper Devonian (II, p. 431) 

 shows the northern limits of water as possibly existing to the 

 line located by Willis. A possible extension of water on the 

 east is shown about to the limit of sediments indicated on the 

 present map. Continental deposits are not discriminated. A 

 probable water body is shown as existing south of Connecticut 

 and extending possibly northward up the Connecticut valley. 



In 1910 Schuchert published his Paleogeography of North 

 America§ which gave a wealth of detail beyond anything 

 previously published. In the construction of his maps he 

 followed the principle that the shores should be shown as near 

 to the limiting outcrops as is reasonable : that is, the extension 

 of the seas to the limits set by Schuchert is practically certain, 

 but. as is noted by Schuchert (p. 116), this method may err on 

 the side of too much restriction of the continental seas. Fol- 

 lowing this method in his map of the Upper Devonian (pi. 77) 

 the shore is shown on the north where it is drawn by Willis. 

 The Catskill Mountain area is shown as an estuary (see p. 545) 

 separated from the sea by a barrier. The necessity of a sea- 

 way for the migration of faunas causes him to locate a strait 

 across northern New Jersey, making the Skunnemunk con- 



* Second Geol. Surv., Pa., vol. G-2, 1880. 



f Second Geol. Surv., Pa., vol. F, Appendix B, 1878. 



% Geology, Earth History, II, III. 



§Bull. Geol. Soc. Am., xx, 427-606. 



