Lewis.] 4^C5 [May 15, 



and are shown abundantlj' at the house of James McFall in the acljoining 

 "woods, and on the road near a cross-road, at a small creek half a mile 

 east of New Prospect. A large boulder of diabase, five feet long, lies 

 opposite the house of J. Brown (formerly W. G. Hutchinson), and shows 

 the approximate position of the dyke where crossing the main road south 

 of New Prospect. 



The trap is again well show^n in the meadow of J. K. Newell (formerly 

 Pollock), where crossing North-East creek at the boundaries of West 

 Nottingham and East Nottingham townships. The dyke crosses the creek 

 less than a mile southeast of Nottingham P. O. From here southward, 

 the trap boulders are known as "Niggerheads." In West Nottingham 

 township the dj^ke once more enters a serpentine region and is here no 

 longer well marked as a separate and distinct dyke. A number of out- 

 crops of diabase occur in this serpentine region, as also a number of other 

 eruptive rocks, including several coarse grained amphibolites and diorites 

 of older geological age. At the chrome mine of Moro Phillips, opposite 

 Pine Grove School-house, there is a small dyke of diabase some five feet 

 wide, which is, perhaps, a branch of the long dyke. Numerous boulders 

 and fragments of diabase occur at the crossing of the Baltimore Central 

 Railroad by the first road north of the Maryland State line. On approach- 

 ing the State Line Station coarse grained eruptive rocks appear, as also 

 large masses of ligniform anthrophyllite ; from here southward, in Mary- 

 land, numerous ancient amphibolites, gabbros, etc., occur, probably being 

 of the same age as similar rocks in the vicinity of West Chester. 



The dyke, probably, enters Maryland a little west of State Line Station 

 (Penn Mar) on the Baltimore Central Railroad. It has not been traced 

 beyond the borders of Pennsylvania. 



Although of remarkable uniformity of texture and composition through- 

 out the whole of its course, this long dyke has, as we have seen, received 

 various local names. While the name "iron stone " is probably most com- 

 monly applied to it, the trap boulders are called " mundocks " in Bucks 

 and Montgomery counties, "camells" in Chester counter, and "nigger- 

 heads " on approaching the Maryland border. 



A carious bit of history, for the accuracy of which, however, the writer 

 cannot vouch, may be introduced in this connection. It is said that the 

 dyke was used during the late war of the Rebellion by the negro slaves as 

 a guide in their flight northward. Several of the stations on the " Under- 

 ground Railroad " are stated to have been on or near the line of this dyke. 

 It is said that the negroes were directed to follow these black rocks across 

 fields and through woods until they were led into the hospitable regions 

 of Chester and Bucks counties. 



Among the many features connected with this long dyke, are the metallif- 

 erous deposits which are due to it. Mention has been made of the pyrite 

 or chalchopyrite sometimes observable to the naked eye, and of the crusts 

 of iron oxide produced as the trap decomposes. The microscope also re- 

 veals an abundance of magnetite in the thin section. It is natural there- 



