1896.] NATURAL SCIENCES OF PHILADELPHIA. 207 



the case on his working township map of Cain about two miles 

 west of Downingtown. 



It is only ftiirto remark that, in the nature of things, much must 

 be discovered as time goes on which was not observed by the last 

 field geologist. New cuts are made, obscure outcrops are made dis- 

 tinct by continued weathering, etc. ; yet it is also true that different 

 observers may give different values and interpretations to the same 

 phenomena. 



The writer added many dykes of trap to those already recognized 

 in geological maps before his work began, but he refrained in a 

 great many instances from connecting together scattered locali- 

 ties where trap fragments occurred, on the assumption that these 

 represented a dyke, because he was often unable to assure himself that 

 these fragments were anywhere near the place of their origin, or 

 uncertain which of the many scattered- localities should be joined. 

 In a country so much denuded as that of Chester Co., Pennsylvania, 

 and where collections of surface fragments of trap occur so frequently, 

 it is generally hazardous to indicate their relations to each other 

 without more substantial grounds than mere geographical position. 



As a matter of fact, a very large number of such indications 

 which appear on the writer's field maps were never transferred to 

 his final geological map, and in some cases not alluded to in the 

 text, because of the difficulty of ascertaining whether or not they 

 possessed real importance. 



March 17. 

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

 Twenty-eight persons present. 



March 24. 



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



Twenty-nine persons present. 



The death of Samuel H. Gilbert, a member, March 20, was 

 announced. 



March 31. 



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



Thirty-six persons present. 



The death of Jean Gundlach, a correspondent, March, 1896, 

 was announced. 



