446 PROCEEDINGS OF THE ACADEMY OF [1892. 



If for CoDslioliocken in the text, Spring Mill, a mile and a half 

 below Conshohockeu, be read, the facts stated agree with these obser- 

 vations, but with the statements in the foot note these observations do 

 not at all accord. 



1, The South Valley Hill does not end at Conshohocken ; on the 

 contrary it extends eastward nearly three miles, as correctly repre- 

 sented on Mr. Hall's map in Report, Vol. O and apparently ends in a 

 spoon above the limestone, as in turn does the latter above the Cam- 

 brian sandstoneand the Cambrian above the Laurentian. This is about 

 a half mile nearly north of Marble Hall ; the exposures are many 

 and clear, and the ending is in a very conspicuous hill which com- 

 mands an extended view westward. 



2, The southern quartzite does not end at the Schuylkill. As 

 this has been repeatedly stated in the reports of the survey, and as 

 in this last report, the non-existence of the Cambrian south of the 

 limestone, west of the Schuylkill, is reiterated, in spite of proof here- 

 tofore adduced before the Geological and Mineralogical Section of 

 the Academy, he would ask attention to the specimens on the table, 

 from various localities within the area in which the Cambrian sand- 

 stone is recognized, and also from the " thin outcrops " which 

 " amount to nothing" along a line, the direct lineal continuation of 

 the Barren Hill-Spring Mill outcrops, and at distances from the 

 Schuylkill of respectively: — GulfH; County Line 2; Stackers 

 25 ; Hare's 21 ; Fenimore's 3i ; Wayne 4 miles southwest of the 

 river. 



This line is directly south of a line of limestone outcrops, precisely 

 as is that east of the Schuylkill. 



It is true that the exposures are scattered and the stratum narrow, 

 but, except the specimen from northwest of West Chester, there 

 can be no doubt that the rock is in place, and as to its absolute 

 identity, no one who examines the specimens can be in doubt. That 

 the belt is narrowing westwardly is shown by a com[)arison of the 

 Barren Hill with the Spring Mill outcrop, besides which he believed 

 that the schists of Cream Valley belong to the same horizon, 

 resembling as they do those occurring between the Cambrian sand- 

 stone of the North Valley Hill and the limestone of the Chester 

 Valley. These schists are colored on Dr. Frazer's map in C* as 

 azoic schists, etc., the same color is given the Laurentian north 

 of the Cambrian, though he could not believe that this was Dr. 

 Frazer's intention. In one of the areas thus colored, the great 

 quarries northwest of Pomeroy have been opened, whence much 

 stone has been obtained for recent work in Philadelphia by the 

 Pennsylvania Railroad. This rock is the typical Cambrian sand- 

 stone of the region. There were specimens of it and of the schists 

 on the table. 



The limestone referred to as flanking the Cambrian west of the 

 Schuylkill, and on its north side, occupies the floor of the narrow 

 valley, locally known as Cream Valley, deep, with steep slopes near 



