1884.] NATURAL SCIENCES OF PHILADELPHIA. 259 



Here we first pass some 200 feet of a soft greenish clay, which 

 rises as walls 20 feet high. Fragments of the serpentine rock, on 

 the surface above the railroad cutting, showed it running into 

 unchanged diorite. .Lying next to the serpentine rock was 50 

 feet or more of both compact and cellular quartz, standing upon 

 edge, and striking to the northwest. It was completely impreg- 

 nated with minute specks and octahedrons of magnetite, which 

 exhibited their decomposition by numerous minute cells filled 

 with iron oxide. The cellular quartz, associated indiscriminately 

 with the compact, was literally honeycombed, the great cells 

 being partially filled with ochrey powder. West of the quartz 

 occurred a thinner development of the serpentine, offering the 

 same features as before. With these facts, we are led to regard 

 the exposure before us as a highly changed dioritic dike, in the 

 centre of which is a huge mass of ferruginous jaspery quartz, from 

 which we interpret the structure of the whole hill. Attaining the 

 sumniit, we find several large pits worked for iron ore. One of 

 them, wrought by George Whitaker, has walls of soft greenish 

 serpentine earth rising some 40 feet, in which are imbedded 

 bouUlers and fragments of cellular ferruginous quartz and iron- 

 stone, together with a considerable admixture of ochrey powder 

 and granular limonite. The economic value of the workings con- 

 sists in washing the serpentine earth, and extracting the limonitic 

 materials. Near the wash-house the yellowish green rock is seen 

 to outcrop with a strike to the northwest. Several of the pits on 

 the hill offer much the same features, while some of them contain 

 a greater abundance of the boulders of cellular quartz. The 

 method of formation of the crusts of iron-stone may be deter- 

 mined by an examination of the numerous quartzose boulders. It 

 consists in the segregation of iron oxide as tortuous veins 

 within the substance of the rock, set free by the complete disin- 

 tegration of the latter ; while the powdery and granular limonite 

 has resulted from an oxidation of the magnetite which so com- 

 pletely impregnates the jaspery quartz. Associated with the 

 boulders of trap, are certain foreign materials belonging to the 

 drift. Imbedded within the serpentine earth of Whitaker's pit, 

 are several large decomposed boulders of granite. Upon the 

 summit of the hill, a large boulder of dark limestone was also 

 found, besides various other materials belonging to th,e boulder 

 drift so universally scattered over the State, 



