DISTRIBUTION OF ROCKS OF THE REGION o&6 



the areal distribution, and the dip lessens to between 10 and 30 degrees. 

 The exposures within this area, which rises to the level of the Piedmont 

 plateau, are not good, and it is not possible to make a detailed correla- 

 tion of any of the beds found within it. The facts observed, however, 

 clearly indicate that we have here, as is so often the case, an anticlinal 

 zone which plunges downward at either end. The best exposures of 

 the formation are those along the northern part of Park Heights avenue 

 between Eccleston and the road from Pikesville to Rockland, which is 

 known locally as the " Old court road." 



The eastern half of the Baltimore gneisses on the southern borders of 

 the area extends from the north and south fault along the Northern 

 Central railroad between Hollins and Sherwood eastward to Towson, 

 and thence across the Gunpowder river to the vicinity of Glenarm, where 

 it terminates in a steep, tightly pinched anticline. On the south the 

 limits of the Baltimore gneiss have not been entirely worked out, but 

 the detailed mapping of the late Professor Williams would indicate that 

 it is bordered by the quartzite which extends from the Northern Central 

 railroad near Mount Washington to lake Montebello, within the north- 

 eastern limits of the city of Baltimore, where the crystalline rocks are 

 covered by the later unconsolidated deposits of the Coastal plain. On 

 the east this formation is bordered at first by the quartzite and lime- 

 stone, but these successively pinch out within a mile or two of the eastern 

 nose of the anticline, and do not appear along the deeply cut trench of 

 the Big Gunpowder river. It is probable that the southern limit is a 

 a strike fault or the contact with the large gabbro mass which extends 

 in a northeasterly direction across Maryland from the eastern limits of 

 Baltimore city to the Susquehanna river near Darlington. Throughout 

 this region of Baltimore gneiss the exposures are poor, due to the 

 high state of cultivation of the land, its plateau-like character, and the 

 presence of numerous well kept country estates. There are, however, 

 numerous exposures along the Gunpowder and in some of the other 

 streams, but the gneisses at this point are intricately penetrated by nu- 

 merous granitic and grabbroic intrusions. 



Northern area. — The northern area of Baltimore gneiss is broadly an 

 ellipsoidal mass, representing a large anticlinal dome, which, like the 

 smaller one of the south, plunges at either end. This plunging of the 

 anticline to the westward brings the overlying formation down to the 

 surface of the country, and thereby causes the surface exposure of the 

 Baltimore gneiss to narrow rapidly to the westward of the Northern Cen- 

 tral railroad. The marked differences in character between the quartzites, 

 limestones, and Wissahickon schists allow the working out of the struct- 

 ure in greater detail than is possible in the eastern half of this anticlinal 



