11 



pebbles are limestone, the cement consisting chiefly of red 

 argillaceous earth. 

 2. Red argillaceous sandstones and red shales. Towards the 

 lower part of the formation, contains numerous beds of 

 coarse gray arenaceous sandstone. 

 Lower Secondary Rocks. 



1. A light blue and gray fossilifcrous limestone — the lower 

 member of formation VJII. of the Appalachian series — ex- 

 tends between Carpenter's Point and Wallpack Bend. 



2. Red and variousl)'^ coloured argillaceous shales. Passes 

 into a heavy compact red sandstone. Occupies the north- 

 western base of the Blue Mountain. 



3. A compact, white and gray sandstone alternating with 

 massive layers of white quartzose conglomerate — the princi- 

 pal rock of the" Blue Mountain. 



4. A dark argillaceous shivery slate, sometimes including 

 beds of roofing slate. Kittatinny Valley. 



5. Blue limestone — presenting -great diversity of aspect and 

 composition — southeast side of the Kittatinny Valley and its 

 branches. 



G. A white quartzose sandstone, somewhat coarse and friable. 

 Occurs only in a few isolated localities. 

 Primary Rocks. These are, almost exclusively, of the stratified 

 class ; consisting of gneiss under all its forms — the grani- 

 toid variety greatly predominating. Innumerable small veins 

 of felspathic granite, sicnite, &c. penetrate the gneiss. 



In offering a systematic description of the geological pheno- 

 mena of a region, we have our choice either to begin with the 

 deposits of a recent date, referable to easily explained causes, 

 passing successively to those of more remote eras and obscurer 

 origin, or to commence our history with the earlier occurrences 

 of our globe, and trace them in their natural order of succession. 



As the latter method seems the one best adapted to our present 

 object, which is not merely to describe the characteristic geolo- 

 gical features of the region, but to unfold, in correct chronologi- 

 cal order, the successive stages through which it has passed in 

 acquiring its present complicated structure, I shall adopt it in 

 these pages. 



