Lewis.] 446 fHIaj. 15^ 



Immediately south of Marslialton, from wliicli place north-eastward for 

 nine miles the dyke has been perfectly straight and continuous, there is a 

 slight bend, or perhaps a small jog in the dyke, as it bends slightly to the 

 south. It is readily traced on all the roads in this vicinity. 



In Newlin township the dyke is again associated with a belt of serpen- 

 tine. Beginning just north-west of North Brook Statjon on the Wilming- 

 ton and Reading Railroad, it runs into a serpentine belt, a mile or more in 

 length, which lies north-east and south-west, and which is famous by 

 reason of valuable corundum mines on its northern flank. The dyke 

 apparently cuts through, the center of the serpentine ridge. An altered 

 granitic rock adjoins the serpentine, and contains a large number of in- 

 teresting minerals associated with corundum. The latter occurs both mas- 

 sive and in crystals, and in masses more or less altered into damourite, 

 etc.,* and appears to be of contemporaneous origin with the serpentine. 



The trap dyke enters East Marlborough township, one-half mile north- 

 east of Uuionville, and passes immediately west of that village, being 

 seen at the fork of the roads, under the bed of a small stream which forms 

 the headwaters of Red Clay creek. Entering west Marlborough town- 

 ship near the village of Upland, large fragments of trap are seen, at the 

 limestone quarries, west of Upland, on the State road. Tbe line crosses 

 the State road at the farm of B. Maule, one mile west of Upland, forming 

 a distinct ridge. 



South-west of here it is finely shown where crossing a north and south 

 road one mf.e north- west of Woodville. It passes under tlie house of Mrs. 

 Rebecca Levis, half a mile north of the Street road, and for some distance, 

 the road runs along it affording a good exhibition of it. Huge boulders 

 of diabase line the road and are built into the fences and into the walls. 



Several small jogs apparently occur in the dyke in the vicinity of Up- 

 land. Such jogs are to be expected in a crack in the earth's crust of the 

 length here described. From here, nearly to the Maryland border, how- 

 ever, the dyke appears to be perfectly continuous. 



Continuing south-west, the dyke crosses the Pennsylvania and Delaware 

 R. R., close to the crossing of the Street road, and entering London Grove 

 township on the farm of ]\Iiffliu J. Baker, it here seems again to divide 

 hornbleudic and syenitic older gneisses from the micaceous schists and the 

 quartzites which cover the country to the north-west. It crosses a small 

 creek, the east branch of White Clay creek, south-west of here ; is well 

 shown in a north and south road in a wood ; passes through the farm of 

 J. Speakman and crosses the Gap and Newport turnpike, one-half mile 

 east of the Londonderry township line. 



Passing south-west af.ross a farm once owned by P. McNelly, it reaches 

 the middle branch of White Clay creek near the corner of Londonderry, 

 Penn and London Grove townships. 



In the high regions covered by decomposed schists south-west of here, 



*See " Corundum, its alterations and associated minerals." F. A. Genth, Proc. 

 Amer. Pliilos. See., Sept. 19, 1873, also Report B. Second Geol. Survey of Peuua. 



