Fi.izer.] iji4 [-Dec. lo, 



Avine (north of Uowiiingtoii), inul I'liper unci Lowrr UwcliUin, north of 

 the Valley. 



As the promise is not admitteil, neither can be the conclusion, -which is, 

 that: 



(4.) " If the mic(t sc/dxfs were older than the Potsdcuii sandstone, they must 

 have been deposited up to a geofjmphiceil line whicJi is sharply defined." 



It does not seem that this follows ; but the suggestion about the geo- 

 graphical line opens the door at once to another explanation of -which the 

 grounds will he more fully stated presently. 



This hypothesis is : That a fault line runs along the South Valley Hill, 

 bringing up the lower pre-Potsdam schists and Laurentides. That this 

 fault does not continue to the extreme eastern point of the synclinal, but 

 leaves it near the eastern extremity, and pursues a course a little to the 

 south of the latter, thus cutting off the southern extension of the Potsdam, 

 but necessarily leaving a part of the northern sheet which, laid down un- 

 conformablj^ on Laurentian and Huronian, has been subsequently eroded 

 from the former except along the Bound Brook Branch R. R. This hy- 

 pothesis is offered, with all modesty and reserve, simply from an inspec- 

 tion of Mr. Hall's map, and without personal study of the ground. But 

 at least it seems possible that that which has happened to the limestone 

 beds, -when the fiiult passed through them, might happen to the enclosing 

 Potsdam when its direction was through the latter. 



(5.) "Even supposing a fault which in all probability docs exist along 

 their northern edge, there rcould still be some remnants of these rocks to be 

 found in their normal position upon the syenites of the Third Belt, andfreig- 

 ments of the rapidly disintegrating schists would have been entombed in the 

 Potsdam sandstone itself, even supposing them to have been swept off the un- 

 derlying rocks north of the present limit." 



It seems evident that the conditions are very different here from those 

 which obtain in Chester and further west. The Susquehanna River sec- 

 tion illustrates at Tocquan creek just the state of things spoken of here. 



The axis of this great anticlinal where, without any doubt whatever, 

 the lowest rocks on this river, within the limits of the State, are exposed, 

 consists of a gneiss nucleus on which lie chloritic and hydro-mica, and finally 

 (where- Potsdam might be expected) quartz schists or schistose-quartz 

 slates. 



Mr. Hall's own definition of his " Edge Hill rock," too, would seem to 

 render it unnecessary to cite examples elsewhere. He defines this rock, the 

 type of his Potsdam, to be "usually a. fine-grained white or gray sand- 

 stone and quartzite, ^cit.h scales of light-colored mica. It is usually thinly 

 laminated. Occasional beds of fine conglomerate are met with." (p. 45.) 



What better example of the entombed remains of the underlying schists 

 could be expected ? If the beds are thinly laminated, it is evident that the 

 materials out of which they are composed were greatly broken up, and 

 nothing would remain of the fschists under the circumstances but the mi- 



