REVIEWS 315 



not show the topographic regularity which the structure has imposed 

 upon the inner zone, yet it has a deal of relief, being made of block- 

 like mountain masses, flat-topped, of nearly equal elevation, nowhere 

 rising into peaks, and separated bv rather broad valleys, so giving an 

 arrangement of two or three ranges of hills with the general northeast- 

 southwest trend. 



The third area, the Piedmont plain, has an undulating surface, 

 sloping to southeast, yet interrupted by conspicuous ridges, one of 

 which fronts the Hudson as the Palisades. These ridges are outcrops 

 of trap, and represent dikes or flows of igneous rock. 



The coastal plain is coincident with the Cretaceous and later 

 deposits. In the description of all these zones, plates are given, show- 

 ing various cross-sections drawn to scale, very helpful in getting a clear 

 conception of the actual topographic conditions. 



With such a complex structure, erosion has ever been busy, and by 

 the differential erosion, and deposition, a basis is given by which the 

 ever-varying attitude of the land is put on record. This very complex 

 history Professor Salisbury and his assistants have deciphered for the 

 long lapse of geologic time since the Triassic, so a tolerably con- 

 nected history is given us from the beginning of Cretaceous time, and 

 the ups and downs on record in this area give a very vivid conception 

 of the instability of the earth's crust or the ocean level, or both. 



There was a post-Triassic uplift when the Schooley peneplain was 

 formed ; then a Cretaceous subsidence and considerable deposits 

 formed; then a slight post-Cretaceous uplift; then a Miocene sub- 

 mergence and more deposition ; another elevation and the formation 

 of the great Kittatinny and other valleys, and the emergence of the 

 Palisades by differential erosion; another submergence — the Pensau- 

 ken — when a broad sound extended from New York Bay southwest to 

 the Chesapeake, and the coastal plain was only half above the sea, as a 

 fringe of sandv islands; then a slight uplift and further erosion, dur- 

 ing which time the glacial epoch brought its mantle of ice to the mid- 

 dle of the state, slightly masking the detail of the topography by 

 erosion and deposition of drift; during which time also the southern 

 half of the state was submerged ; lastly, a postglacial elevation to pres- 

 ent altitude. 



This long record is made out by the most careful study of the 

 physiography, by the intelligent mapping and correlation of a vast 



