the Middle Atlantic Slope. 379 



ware respectively, Delaware river and bay are flanked on the 

 west from Philadelphia to Dover by a deposit of brick-clay or 

 loam passing into gravel below — the Philadelphia Brick Clay 

 and Red Gravel of the former author, and the Delaware Grav- 

 els of the latter. The deposits have been described in detail 

 by these authors, and it will suffice to add that not only in gen- 

 eral characters but in the less conspicuous features detectable 

 on minute examination they are unclistinguishable from their 

 homologues in corresponding position on the Susquehanna and 

 Potomac ; the structure and composition are similar, the geo- 

 graphic and hypsographic distribution are alike, there is equal 

 lixiviation and ferrugination, like ravining by erosion, the same 

 'extensive terracing, etc.; the only noteworthy difference being 

 the somewhat greater altitude of the Delaware deposits, and 

 the occasional presence of far transported northern pebbles and 

 bowlders in their lower portion. 



JSTorth of Philadelphia the Delaware deposits exhibit certain 

 noteworthy characteristics allying them with those of the upper 

 Susquehanna. Over the gentle river-ward slopes of eastern 

 Montgomery and Bucks counties, Pennsylvania, more or less 

 conspicuous accumulations of loam or brick clay occur up to 

 altitudes of 250 feet or more ; and well rounded bowlders oc- 

 casionally appear at even greater altitudes. Within 100 feet 

 above tide the deposits are practically continuous and exten- 

 sively terraced — e. g., there is at Trenton a sharply defined 

 terrace 80 feet in altitude composed of homogeneous brick clay 

 passing downward into a bowlder- bed, through which the 

 Delaware has cut its modern gorge ; and the celt-yielding 

 Trenton gravels fill a basin lined with these older Quaternary 

 deposits. Still farther northward the brick-clay or loam, with 

 associated cobbles and bowlders, are found at progressively in- 

 creasing altitudes ; they occur in every in+er- montane valley on 

 the Delaware to the terminal moraine at Belvidere ; and they 

 are found on both sides of the Lehigh from its mouth to the 

 water gap, the loam being largely utilized in brick manufacture 

 at Allentown and elsewhere. 



The cross-section of the Delaware valley five miles below 

 Belvidere is in all essential respects a du23licate of the Blooms- 

 burg-Berwick cross-section of the Susquehanna showm in fig. 

 1 : there is the same loam-lined base-level valley 200 to 800 

 feet above the river, with scattered quartzite bowlders up to 

 at least 400 feet ; within this valley there is excavated, through 

 loam and subjacent rock, an outer gorge at least a mile and a 

 half wide ; this outer gorge is bottomed with well rounded and 

 current-sorted overwash gravels from the terminal moraine; 

 and the sharply cut inner gorge of the present river, quarter 

 of a mile wide and 50 feet deep, has been carved in the newer 



Am. Jour. Sci.— Third Series, Vol. XXXV, No. 209.— May, 1888 

 23 



