206 * PROCEEDINGS OF THE ACADEMY OF [1896. 



March 3. 



The President, Samuel G. Dixon, M. D., in the Chair. 



Two hundred and fifty-eight persons present. 



Messrs Morris E. Leeds and J. S. Stokes of Messrs Queen 

 & Co. gave a resume of investigations relating to Roentgen photo- 

 graphy and a demonstration of the processes employed. (No 

 abstract). 



March 10. 

 The President, Samuel G. Dixon, M. D., in the Chair. 

 Forty-nine persons present. 



Papers under the following titles were presented for publication : — 

 " Summary of New Liberian Polydesmidse," by O. F. Cook, was 

 presented for publication. 



" The Minerals of South Carolina," by J. G. Hartzell, Jr. 



Two Supposed Nero Trap Dykes in Chester County, Pennsylvania. 

 — The following communication was read from Dr. Persifor 

 Frazer : — 



In a paper read before the Academy, Feb. 1, 1896, Mr. Theo. D. 

 Rand calls attention to two trap dykes which he thinks have thus far 

 escaped notice. The writer is unable to ascertain by the localities 

 to which Mr. Rand refers, the beginning of the one said to be in the 

 northern half of the County, viz. : " Williams' Quarry, near Aldham." 

 The trap is called " a jDeculiar porphyry * * containing the variety 

 of silica Vetsan ; " and it is said that " a rock which Mr. Goldsmith 

 has pronounced identical occurs near Barneston Station on the 

 Waynesburg branch of the Penna. R. R." In the working town- 

 ship map used by the writer in his field studies of the geology of 

 Chester County, is found noted a porphyritic quartzose syenite. In 

 Report of Progress, Second Geological Survey of Pennsylvania, 

 Volume C 4, p. 248, 3d paragraph from bottom, a quartz porphyry 

 is also noted as visible in j^lace probably about half a mile south of 

 Barneston Station. 



The second dyke which begins in Downingtown is probably the 

 same to which the following reference is made (same volume, p. 

 274). " At several points on the road leading south from the 

 Downington R. R. station occur fragments of trap." 



Again just south of the northernmost apex of West Marlboro' town- 

 ship and within a short distance of Doe Run the existence of trap 

 is noted on the working field township map of the writer, as is also 



