THE 



JOURNAL OF GEOLOGY 



MAY-JUNE, 1908 



FEATURES INDICATIVE OF PHYSIOGRAPHIC CONDI- 

 TIONS PREVAILING AT THE TIME OF THE 

 TRAP EXTRUSIONS IN NEW JERSEY 



C. N. FENNER 



The Watchung Mountains form prominent features in the topog- 

 raphy of Northern New Jersey. On account of the great hardness and 

 erosion-resisting quaHties of the rocks composing them, they rise well 

 above the surrounding shales and sandstones and add much to the 

 beauty and picturesqueness of this portion of the state. 



Their geological features and their relation to the adjacent strata 

 have been the subject of study since the early years of the last century. 

 Views regarding them have changed greatly. New facts have been 

 brought to light and the interpretation of the observed conditions has 

 changed with the advance of geological science. Gradually, however, 

 a close agreement has been reached in the conclusions of various 

 observers with regard to the major features of their structure and rela- 

 tions, and in brief form it may be said to be held that these three ridges 

 are the remnants of three successive flows of lava which were poured 

 out as great sheets over the surface of beds of sandstone, or similar 

 material, which was in course of deposition at the time. After each 

 flow the process of deposition of the sandstones was resumed until 

 interrupted by the next flow. Later the whole series of sandstones 

 and intercalated traps was shghtly tilted so as to form a monocline 

 with gentle western dips, and the edges were eroded and carried 

 away. The trap sheets, on account of their resistant qualities, were 

 Vol XVI, No. 4 299 



