Frazer.J OiO Dec. 15, 



North of the giieissoid schists again the quartzite dips about S. Vfi £-452, 

 and tiierefore underlies these schists while the limestone either abuts upon 

 them or overlies them in a sharp upward curve, which can no longer be 

 traced. 



(2.) The objection to tlie mathematical straigiitness of the line of junc- 

 tion of such soft rocks as the hydro-mica schists and the limestones is a 

 serious one. Nothing is more likely, on the otlier hand, than that such a 

 mathematical line of demarcation should be established by a line of 

 fracture. 



(3 ) The absence of limestone from the junction of the Potsdam and the 

 schists from Huntingdon Valley eastward on Mr. Hall's map, is dithcult to 

 explain if these schists reall}'^ belong above the limestone, and there be no 

 fault along this line. If on the other hand there be a fault (which natu- 

 rally extends along the South Valley Hill), it is singular that it does not 

 bring up the underlying limestone and broaden that valley if the schists 

 of the South Valley Hill are superior to the limestone. 



(4.) The limestone of Adams, York and Lancaster counties believed to 

 be No. II of Rogers is much mixed with schistose and micaceous matter in 

 its inferior layers and is usually surrounded by schists from which this 

 foreign matter is derived. 



The limestone of Chester county, near Stottsville, Pomeroy, Parkes- 

 l)urg, and for the whole length of the Chester Valley, is similarly mixed 

 with micaceous matter and frequently resembles a mica schist more than a 

 limestone. 



(5.) TJiePotsdam^uartzite and sandstone near Coatesvilk are similarly 

 mixed with micaceous material, and this texture may be very frequently 

 observed in the lower layers of the Potsdam elsewhere in Chester as well 

 as where Mr. Hall has observed it. 



(6.) The contact of the limestone sometimes with the Potsdam and 

 sometimes, when the latter is al)sent, with the schists, may be observed in 

 lower Lancaster and apparently on the southern side of the great 

 (Tocquan ?) anticlinal which passes through Sadsbury townships of 

 Chester and Lancaster counties. 



(7. ) In various places in East and West Brandy wine and Lower Uwchlan, 

 chlorite and hydro-mica schists are abundant below the Potsdam. The 

 series is well exposed from a short distance north of the E. Cain border 

 on the North Branch of the Brandy wine past Dowlin's Forge and Dorian's 



Mills. 



(8.) If the schists south of the Chester Valley be younger than the 

 limestone, and the Doe Run and Chester Valley limestones represent but 

 one horizon, there must be a synclinal fold between the two. 



But it has been stated above that the dips are tlatter towards the south, 

 so that if there l)e here a plication, it is an anticlinal. 



