24 ANNALS NEW YORK ACADEMY OF SCIENCES 



Map both provide structural cross-sections of the region. Essays by 

 Davis (136, 137, 138) on the geographical development of northern New 

 Jersey and on the dates of origin of topographic forms on the Atlantic 

 Coast, and reports by Kummel (141, 142) of the New Jersey State Sur- 

 vey, as well as other New Jersey (254, 256) reports on the physical feat- 

 ures of the State, should be looked over. Consideration on this trip would 

 be given to the formation of vertical cliffs in resistant formations, the 

 Cretaceous peneplane, the origin of the Hudson Eiver, the alluvial ter- 

 races, notches produced by cross-faulting, and also to the matter of 

 glaciation. 



Inwood and Bronx Park. — A third half-day trip will include a study 

 of the Dyckman lowlands (Fig. 14), the anticlinal limestone valley 

 through which Broadway runs, between the Fort Washington and Fort 





Hp Second Mtn. 



Blue. Mt-n. 



•Susquehanna Water Gap 



gb St*^- ■-:■:-■:.■:: .^r— ^- _ 





Fig. 21. — The great stone arch bridge of the Pennsylvania. Railroad at the 

 Susquehanna Water Gap 



The piers of the bridge are built upon the same hard formation which makes up the 

 Blue Mountain. Owing to its resistance, this rock occasionally outcrops in the river 

 and forms a series of rifts or rapids, which is true also of most of the other ridge-form- 

 ing strata. 



George Heights, tran verse faulting in the New York City region, the 

 youthful gorge of the Bronx Eiver with its pot-holes, the mature upper 

 portion, small subsequent valleys in the Manhattan schist, glacial striae, 

 and erratics of Palisade trap. Folio 83 should be studied and articles 

 by Hobbs (45, 46, 47) on faulting and by Kemp (49) on the Bronx 

 River should be kept in mind. 



One-Day Trips 



Watchung Ridges. — A profitable one-day's excursion will be a study 

 of the Watchung Ridges at Plainfield, N. J. (Fig. 29). The necessary 

 topographic maps, the Passaic Folio, and the New Jersey Geological Map 

 should be on hand. Articles of reference will include essays by Davis 

 (136, 137, 138) on northern New Jersey; also articles by Lewis (143), 

 Kummel (141, 142), Salisbury (144), and Darton (134). The day's 

 study is devoted to a consideration of trap ridges, water and wind gaps, 



