228 PROCEEDINGS OF THE ACADEMY OF 



Weathering of Bocks. Prof. Persifor Frazer, Jr., remarked 

 that the igneous rocks in tlie vicinity of Gettysburg, Pa., present 

 some curious phases of weatliering. The ridge along which our 

 forces were disposed during the battle at that place, consists of a 

 syenite which at a point opposite the position of our army's ex- 

 treme left wing (or Kound 'J'op) has broken off, and lies in huge 

 bowlders piled up with great irregularity, and presenting surfaces 

 sometimes many hundred yards in area. These surfaces are some- 

 times furrowed by channels cut into them by running water, and 

 intersecting in all directions so as to present the general appear- 

 ance of a Cyclopean wall. The furrows are about an inch in depth, 

 and the raised surfaces which they separate, though slightly dis- 

 colored, present no signs of perfect disintegration. The similitude 

 to a coarse wall built up of fragments of all sizes, is striking and 

 deceptive even on a close examination. 



In some cases, this entire furrowed surface is detached b^' a frac- 

 ture, wliich separates it as a mask from the normally constituted 

 mass beneath it, and in a few instances there were observed two 

 such shells one beneath the other. 



Tliis gave the whole rock a concretionary appearance wliich was 

 remarkable for the tolerably constant thickness of the shells, con- 

 sidering the want of homogeneousness of the rock. It raises an 

 interesting question of how rocks may assume this character by 

 weathering alone. 



December 29. 

 The President, Dr. Ruschenberger, in the chair. 

 Twenty-six members present. 



Isaac S. Williams, R. M. Girvin, M.D., George I). McCreaiy, J. 

 Elmore McCreary, and Robert B. Cruice, M.D., were elected 

 members. 



Capt. J. H. Mortimer and M. C. Cook, of London, were elected 

 Correspondents. 



The following reports were read and referred to the Publication 

 Committee : 



THE LIBRARIAN'S REPORT. 



The Librarian respectfully reports that IGfiO additions have been 

 made to the library during tiie year 1814, being an excess of 324 

 above the number reported for 1873. 



Of these 235 were volumes, 1416 pamphlets and parts of periodi- 



