178 PROCEEDINGS OF THE ACADEMY OF [1893. 



igneous rock in the form of slabs and huge boulders. These were 

 generally called trap by our geological friends, but the people call 

 them ringing rocks ; or, what means the same, klinkstones. The 

 exposure is a large one, but, on inspection it was found that the trees 

 encroach upon it and have already conquered a considerable area of 

 the outcrop. They will probably in time cover the entire locality 

 which is called the Stony Garden by the people who go there on. 

 picnics. 



The klinkstones, as they are called (or, more properly speaking 

 phonolites), produce a metallic sound when struck by a hammer, 

 and the sound differs with almost every block or slab. 



It is known that these rocks are basic in their chemical relations 

 and this fact was fully established by my having, after a careful 

 examination of some specimens, obtained 52*15% of silica (Si0 2 .) 



These phonolites, if not affected by atmospheric influence, are of 

 a dark color ; but they become ash-gray externally whenever exposed 

 to the air. They are tough and mostly fine-grained ; so much so 

 that, macroscopically, it is utterly impossible to determine their 

 mineralogical composition, although, with the aid of the pocket lens, 

 a few crystals may be seen. The thin section (fig. 2) had to be 

 magnified 100 diameters to make the components visible. It was 

 compared with standard rock slides: diallage, plagioclastic feldspar, 

 sanidine, amphibole and magnetite. 



Inasmuch as the composition embodied in these rocks constitutes 

 a gabbro, I have proposed the name gabbro-phonolite for this, the 

 first American phonolite. 



Another dyke of phonolite, of essentially the same character and 

 of nearly the same composition, is exposed in Bucks County near 

 the Delaware River, opposite Holland Station, New Jersey. 



Three miles north of Pottstown, Montgomery County, Pa., is a fine 

 exposure of the same kind of phonolite as described above. The 

 people of the town call it the Ringing Hill. As it is easily reached 

 it is used as a pleasure grove. The encroaching trees will, in all 

 probability cover the entire outcrop, the greater part having already 

 been covered up. 



In PI. II, figure 3, I have tried to illustrate a thin section of 

 gabbro-phonolite collected from the dyke through which the North 

 Pennsylvania Railroad passes. The point is about two miles north 

 of Quakertown, Bucks County, Pa. A description may appear 

 superfluous because the composition is so nearly like the one from 



