DISTRIBUTION OF ROCKS OF THE REGION 355 



ing, as is brought out more clearly by the small stringers of marble found 

 infolded with them. On the end of the anticline to the west the beds 

 change rapidly in strike from east-northeast to northeast, through north 

 and northwest to west-northwest. On the eastern end the strikes of the 

 beds change similarly from east-northeast to northwest, through north 

 to north 45 degrees east, the dips in all cases being away from the under- 

 lying Baltimore gneiss and beneath the overlying marble or Wissahickon 

 schists, as the case may be. 



The eastern exposures of quartzite forming the ridge on the south 

 side of the limestone valley extending from Sherwood to Glenarm are 

 less satisfactory than those just described, but wherever observed indicate 

 a northern dip of somewhat less inclination until near the eastern end 

 of the anticlinal fold, where the beds rise steeply on the north with a 

 northerly dip of 75 degrees and an easterly dip on the south of about 

 40 degrees. The anticlinal character of the structure at this point is 

 usually well brought out for Piedmont conditions by the formation of a 

 triangular hill of quartzite produced by the nose of the fold, which is 

 cut through by Long Green creek about a mile from its apex. The 

 strikes of the quartzite may be traced at this point along the top of the 

 ridge, where they show progressive changes in position through all 

 azimuths from north 45 degrees east, through west and north, to north 

 30 degrees east, and even reach north 60 degrees west near the crossing 

 of the Harford turnpike. The character of the quartzite in this part of 

 the fold is not that typical of Setters ridge, but shows the development 

 of more mica with accessory garnets and occasional cyanite. 



Throughout this entire southern region the quartzite shows the average 

 thickness of about 500 feet. 



Northern area. — Theareal distribution of the quartzite about the north- 

 ern dome of Baltimore gneiss is much less constant than is the case 

 about the southern areas, and there are many evidences of a marked 

 erosional conformity and a few strike faults in this part of the region. 

 The occurrence of the quartzite may be traced almost continuously from 

 a few miles west of the Northern Central railroad near Cockeysville along 

 the southern side of the road to the northeastern nose of the fold on the 

 road between Taylor and Jarrettsville, where a well defined V-shaped hill 

 is formed by the upturned beds of the quartzite, and thence westerly on 

 the northern side of the dome. The quartzite is not distinguished in the 

 cut of the Northern Central railroad north of Monkton, but the typical 

 tourmaline-bearing mica-schist is found outcropping on the hills across 

 the river, and thence may be traced along the westerly side of the dome 

 in several bands to the southwestern nose of the anticline, where it may 



XLVIII— Bull. Geoi,. Soc. Am., Vol. 16, 1904 



