F.. Prime, Jr.—Lower Silurian Fossils. 261 
densed on the object at an angle of 80° to 40°. The photo- 
graph in question was direct, by which I mean that there was 
no intermediate or secondary enlargement of a first photograph. 
With this photograph and the lantern described, I awe shown 
Frustulia saxonica magnified more than half a million diame- 
ters; a result which must be seen to be appreciated. 
Art. XXXVIII.— On the Discovery of Lower Silurian Fossils in 
Limestone associated with Hydromica slates, and on other points 
in the Geology of Lehigh and Northampton Counties, Eastern 
Pennsylvania ; by FREDERICK PRIME, Jr., Professor of Metal- 
lurgy at Lafayette College, Easton, Pennsylvania. 
erles were made lies near the eastern verte of the State, south- 
idge. Th 
ings of the Philosophical Society for December 21, where it appears 
under the title “ On the Paleozoie Rocks of Lehigh and North- 
ampton Counties, Pennsylvania.—s. D. D. 
THE Paleozoic rocks of Lehigh and Northampton counties 
are: The Potsdam Sandstone (No. I); Magnesian or Aurorz 
Limestone (No. II); Trenton Limestone (No. II); Utica Shale 
(No. III); Hudson River or Matinal Slate (No. IIT). | : 
The Potsdam sandstone is first found in the outlying penin- 
sula of the South Mountains, known as Ridge, where it 
Am. Jour. ee Vou. XV, No. 88,—APRIL, 1878. 
