1883.] Geology and Paleontology. 647 
to which he refers. I can with propriety, however, make a few 
comments here on his argument. 
In the first place Mr. Rand does not account for the absence of 
slates, corresponding to the South Valley Hill belt (hydromica 
_ slate), on the north side of the Potsdam sandstone of the North 
Valley hill. 
The Potsdam of the North Valley hill, in the vicinity of the 
Schuylkill river and the sandstone east of the river, rests directly 
upon a series of syenites, hornblendic and quartzoic rocks which 
correspond in age to the rocks of the Reading and Durham hills 
in Lehigh and Northampton counties (Laurentian). 
r. Rand quotes a statement of mine that the “ hydromica 
schists * * * are the Hudson River shales and flank the 
Chester valley on the south.” 
The quotation does not convey the fact that I argued that the 
limestones of the Chester valley rested upon decomposed feru- 
ginous slates with limonite ore and Potsdam sandstone. 
The decomposed slates are without doubt the upper primal of 
Professor Rogers. 
N Primal slate. South Valley hill. 
No Limestone, 
Along the southern margin of the limestone in the district un- 
der consideration (vicinity of the Schuylkill river) the limestones 
pass by gradual alternations into slates (hydromica slates of the 
South Valley hill). 
_ The character of the limestone is very different along the south 
Side of the valley from that on the north. 
long the northern side of the valley there is nothing to be 
Seen of a transition from the the upper primal slates into the lime- 
Stone of No. 1 
Adjoining the alternations of limestone and slate along the 
_ Southern margin of the Chester valley there is no regular deposit 
of an or quartzite in any portion of the district where I have 
Worked. 
The limestones along the northern edge of the Chester valley 
are usually more or less of a light drab color, and decidedly 
dolomitic, while on the southern side of the valley they are usu- 
“y of a bluish cast and associated with white and blue marble. 
The Marble is always confined to the southern side of the valley. 
S a further argument in favor of the superposition of the 
hydromica schists of the South Valley hill, I considered the syn- 
clinal Structure of the north-eastern point of the South Valley 
hill just north of Gulf mill and the synclinal structure of the 
Mill escarpment, 
