Prime. | 248 [Dee. 21, 
On the Paleozoic Rocks of Lehigh and Northampton Counties, Pennsyl- 
vania. 
By FREDERICK PRIME, JR., PROFESSOR OF METALLURGY AT LAFAYETTE 
COLLEGE, EASTON. 
(Read before the American Philosophical Society, December 21, 1877.) 
The Paleozoic rocks of Lehigh and Northampton counties are : 
The Potsdam Sandstone (No. I). 
The Magnesian or Auroral Limestone (No. IT). 
Lhe Trenton Limestone (No. II). 
The Utica Shale (No. III). 
The Hudson River or Matinal Slate (No. IIT). 
The Potsdam sandstone is first found in the outlying peninsula of the 
South Mountains, known as Lock Ridge, where it occurs on the north-west 
flank of the hill and undoubtedly has a north-west dip, those dips observed 
to the south-east being due to a sinking down of the rock at its exposure, 
where the underlying gneiss has been removed. It next occurs in two small 
patches on the northern flank of the main range of the South Mountain 
near Macungie (formerly Millerstown). A small patch of it is also found as- 
sociated with the gneiss, where the latter crops out through the limestone 
in the gorge of the Little Lehigh Creek at Jerusalem Church, two miles 
north-west of Emaus. But it is first seen to any great extent along the 
north flank of the main range just south of Emaus, where its occurrence 
is constant, but of varying thickness, and continues for a distance of four 
and a half miles, after which it can no longer be traced. 
It occurs again at the ridge of the South Mountain, close to Allentown, 
which forms the southern barrier of the Lehigh River, between Allentown 
and Bethlehem, where the sandstone is about twenty-five feet thick and 
extends with a few intervals (where it has been cut out by the river) the 
entire distance between these two places. It also extends across the 
Lehigh and forms the capping rock of a portion of the gneiss just east of 
Allentown and north of the Lehigh. The contact between the gneiss and 
sandstone is distinctly seen about two miles east of Allentown on the Le- 
high Valley Railroad track. 
The very lowest beds of the Potsdam sandstone are actual pudding- 
stones, containing pebbles the size of a man’s fistand larger, and fragments 
of red, unaltered orthoclase. The upper beds are composed of a hard, 
compact quartzite containing greater or less quantities of feldspar nodules, 
which weather out and impart to the rock a pock-marked appearance. 
When first quarried the color of this quartzite is blue to bluish-gray, which 
on exposure soon changes to a dark reddish-brown, due to the oxidation 
of the ferrous oxide it contains. The change from a pudding-stone to a 
compact quartzite in the sandstone shows that there has been a gradual 
