376 W. J. 31c Gee — Three Formations of 



nearly to the river and then dropping suddenly to its flat 

 bottomed gorge, and everywhere except in the sharper ravines 

 and larger tributary valleys the deposits prevail, and the alti- 

 tude to which they rise progressively increases up the river ; 

 within its hypsographic limit the formation in the Susque- 

 hanna valley is nearly as continuous and distinctive as the gla- 

 cial drift of the northern part of the state, and its influence 

 upon the industries of its area is equally important. 



The relations of these deposits to the terminal moraine and 

 the relations of both to the topography are significant, and are 

 well exhibited in the Susquehanna valley about Berwick and 

 Bloomsburg. The broad features of the region, like those of 

 the inter-montane Appalachian valleys generally, comprise old 

 base level plains of considerable uniformity, bounded by moun- 

 tain ranges, sharply incised by waterways cut down to a newer 

 base-level. The principal waterway is the broad, steeply 

 bluffed outer gorge of the pre-morainal Susquehanna. This 

 gorge is partly filled with the overwash gravels from the mo- 

 raine ; and in these gravels the narrow inner gorge of the 

 present river is excavated. 



Three miles above Bloomsburg the old base-level plain is 

 5 or. 6 miles wide, gently undulating, and 200 to BOO feet 

 above the river, which follows its southern side (fig. 1). The 

 entire plain is covered with a sheet of fine loam or brick clay 

 similar to that of Harrisburg, and like it graduating downward 

 into stratified sand or gravel containing well rounded bowlders 

 of quartzite and other sub-local rocks up to a foot or more in 

 diameter. On approaching the river this plain breaks down 

 sharply in an abrupt escarpment, 75 to 100 feet high, over- 

 looking the pre-morainal valley, the loam and gravel extending 

 to the verge of the escarpment but failing below. This outer 



MONTOUR RIDGE 



CATAWISSA HILLS 



Fig. 1. — Cross-Section of Susquehanna Valley between Bloomsburg and Berwick. 



valley of the Susquehanna is perhaps one and a half miles 

 wide, and is lined to an undetermined but considerable depth 

 with rounded pebbles and cobbles, sometimes interstratified 

 with or overlain by fine gravel, sand or loam — the whole rep- 

 resenting the overwash materials from the terminal moraine ; 

 and the valley bottom descends by step-like terraces of won- 

 derfully sharp contour and fresh aspect to the narrow inner gorge 

 within which the river tumbles and dashes over a bed of simi- 

 lar pebbles and cobbles. South of the river the surface rises 



