MARYLAND GEOLOGICAL SURVEY 99 



South of this point the exposures are not good. A fine-grained 

 hornblendic granite-gneiss shows in the soil. One half a mile above 

 Frenchtown the meta-rhyolite is exposed in places. It occupies the 

 valley of the little creek at this point and probably extends to the 

 northwest along the Susquehanna. 



At Frenchtown the granite-gneiss is actively quarried, but to the 

 east and north the rock is meta-rhyolite. This is largely concealed 

 beneath the gravels, but can be seen along the roadway from Aiken 

 to Blythedale and at Blythedale. East and north of this village it 

 is completely buried, but reappears in the neighborhood of Bay Yiew. 

 Here a large body of it, more than a mile in width, strikes to the 

 northeast. It is exposed by the streams which cross this area. It 

 is also well exposed at the junction of the two main branches of 

 Stony Kun, on Northeast Creek and on the Little Northeast, where 

 it appears in a considerable cliff. 



At the former locality, one half mile northeast of Bay Yiew, 

 boulders of the meta-rhyolite are piled up in picturesque confusion. 

 The stream dashes over the rock in a series of cascades which give 

 charm and wildness to the glen. The spot is known as " Gilpin 

 Rocks " and is a resort for picnic parties (Plates II, Fig. 2, and XI). 



Here the prevailing color of the rock is green, though some fresh 

 grey material may be found. A light-colored aplitic rock penetrates 

 it in narrow dikes. Hornblende, chlorite and epidote characterize 

 the green material in the hand specimen. 



In a road-cut on the Baltimore and Ohio railroad just before it 

 crosses Principio Creek, both fresh and disintegrated meta-rhyolite are 

 exposed. It is also uncovered in the bed of Principio Creek to a 

 point within a half mile of Principio Furnace, where it gives way 

 to the enclosing hornblende-granite. 



An offshoot of the meta-rhyolite appears as a dike, about twelve 

 feet in width, at Mechanics Valley. 



The rock was found comparatively fresh in the Susquehanna 

 exposures, in the Baltimore and Ohio Railroad cut and a short dis- 

 tance north of Frenchtown, where it had been blasted in making 

 place for a telephone pole. 



