24 PROCEEDINGS OF THE ACADEMY OF [1886. 



tion was directed to inclusions in certain flaggings in Philadel- 

 phia, on Chestnut Street above Third Street, and on Filbert Street 

 above Thirteenth Street. It was desirable to trace the localities 

 of these rocks. 



By the assistance of the City Commissioner of Highways, and 

 the dealer who furnished the stone for the Chestnut Street pave- 

 ment, the locality was ascertained to be Connecticut or Maine. 



The doubt in the case arises from the fact that the stone was 

 furnished about twenty-five years ago, no record of its locality 

 was kept, and the dealer is unable to recall with any degree 

 of certainty the exact location. The granite in external charac- 

 ters closely resembles that of New London, Conn., as well as that 

 of Sullivan, Maine. Hence this feature is compai-atively valueless 

 in the determination. But the resemblance of the inclusions to 

 those in the Sullivan granite, favors the view that this location is 

 the home of the Chestnut Street flags. 



These inclusions are not numei'ous, nor regular in size and 

 outline. They are made up of biotite, are elongated elliptically, 

 frequently terminating in acute points. The length is eight or 

 ten inches, and the width two or three inches. These masses 

 blend into the surrounding rock, without affording any distinct 

 line of separation, hence suggesting that their extraction would 

 involve considerable difficulty. That these were produced in a 

 way similar to those of Craftsbury, is apparent from external 

 observations, and doubtless sections of the internal structure 

 will sustain this supposition. 



No evidence was obtained concerning the locality of the Filbert 

 Street rock. Its worn condition denotes a long period of service. 

 These inclusions tend to detract from the value of granites, as 

 they afford an easy access for destructive agents (moisture, frost, 

 heat), and hence such granites having a limited use, are not apt 

 to be seen along public thoroughfares. 



