1893.] NEW YOKK ACADEMY OF SCIENCES. 75 



series, and in the other related rocks from the -well-known 

 exi^osures near Baltimore* and in northern Delaware. "j" 



C. E. Hall records also black boulders from the roadside 

 toward Feasterville, and a number of other rocks from the 

 neighborhood, whose microscopic description attracted my 

 attention. Fortunately in the careful methods practiced by the 

 Pennsylvania Survey, as regards their museum material, they 

 were all recorded by numbers, and by the courtesy of Professor 

 J. P. Lesley I have received some chips for thin sections. The 

 " diorite?" No. 5306, is an olivine-diabase, and undoubtedly a 

 stray Triassic boulder. Ries and Fennor found one of much 

 the same character (No. 16). It was only provisionally called 

 by Hall " diorite?" His analysis is quoted below. No. 5309, 

 called provisionally " syenitic gneiss?" contains shattered 

 quartzes, orthoclase and decomposed garnet. The dark silicate 

 is too much altered for recognition, but it probably was horn- 

 blende, Nos. 5305 (" trap ") and 5307 {" black syenitic gneiss ") 

 are both formed of green hornblende in largest amount, with 

 much less plagioclase. They are amjDhibolites rather than trap 

 or diorite, and are doubtless much metamorphosed igneous 

 rock of an original dioritic nature. They are very like our 

 No. 8, which was gathered east of the quarry. The association 

 of such rocks, with norites and gabbros, is known both at 

 Baltimore and in Delaware. The analyses of two of the above 

 numbered specimens yielded the following (5306 is by C. E. 

 Hall, 5309 by F. A. Genth, Jr.); 



* G. H. Williams. Bulletin 28, U. S. Geol. Survey, 

 t F. D. Chester, Bulletin 59, U. S. Geol. Survey. 



