CRETACEOUS PENEPLAIN IN NEW JERSEY. 006 



plane gently inclined toward the southeast and toward the southwest, -s^ * * The 

 new atlas of the state will show how remarkably even-topped these ridges of the 

 highlands are, and enable the reader to construct for himself the plateau indicated 

 here by these crest-lines. ■Jt * * They are not to be understood as level, but as 

 diversified by the ridges which rise from 100 to 300 feet above the deepest depressions^ 

 the latter being 400 to 600 feet above the adjacent valleys and plain country. Once 

 upon them the so-called mountains disappear and sink into hills, whereas when viewed 

 from the valleys, the plateau or table-land rises up as a mountain." * 



Precisely the same arguments that have been used in considering the 

 plateau in New England are applicable here. They lead to the same con- 

 clusion in both cases. The whole region must have once stood at a lower 

 level, and Ions; enouo-h to have been denuded to the then baselevel from 

 whatever earlier constructional topography may have once existed. The 

 structure is one of extreme disorder. The topography commonly associated 

 with such structure is that of mountain ranges, and we cannot hesitate in 

 the belief that a fine range of mountains once existed here. If we would 

 study the form that these ancient mountains once had, we should go to 

 regions of more recent mountain growth, like the Alps ; while if we would 

 discover the structures that characterize the foundations of the Alps, we 

 should look to the New Jersey highlands and their relatives along the At- 

 lantic slope. 



If the observer will ascend the hills on the front of the highland mass, 

 as at Boonton or Morristown, he will see in the east the even crest-line of 

 the Watchung trap ridges in the Triassic formation.f The ridges consist of 

 two lava flows,! separated by one or two hundred feet of red shales. The 

 lava sheets dip westward and constructionally ascend toward the east into 

 the air. If the denudation by which they have been truncated from their 

 once greater extent to their present form had taken place in the present 

 position of the mass with respect to baselevel, it would be difficult, if not 

 impossible, to explain their even summit lines. Here, as in the highland 

 plateau, the denudation must have been in greatest part accomplished while 

 the mass stood lower thau it does now. Crossing the valley of the upper 

 Passaic from the crystalline plateau to the eastern of the two Watchung 

 ridges, and again looking eastward or northeastward, the outline of the 

 Palisades ridge may be seen in the distance. Like the others, it has an even 

 crest-line, but at a lower level. It is the edge of an intrusive lava sheet, 

 tilted like the others to a moderate westward dip and truncated to its present 

 form. Beyond the Palisades and across the Hudson, we come to the grad- 

 ually ascending upland of crystallines, which, if continued, would lead 

 us across southern New York and Connecticut, and into Massachusetts 

 once more. 



♦Geological Survey of New Jersey, Annual Report, 1883, pp. 27-29; .<«ee also pp. (30, Gl. 

 t A view of the front of these ridges, as seen from the lowland on the east, is given in plate 1 of 

 the Annual Report of the Geological Survey of New Jersey for 1882. 

 JN. H, Darton: Bull. 67, U. S. Geol. Survey, 1890, 



