Basalt in Paleozoic Rocks in Central Virginia. 315 



least in the southern Appalachians. Rocks of somewhat similar 

 appearance have been found by the author in various portions 

 of the Archean mass east of the Silurian sediments, but the re- 

 semblance of the two groups is not sufficient to warrant any 

 deductions. Beyond the fact of their eruption through the 

 Silurian sediments and their location upon the great anticlinal 

 regions, there are no facts of distribution which throw any 

 light upon their cause. In one case, at Hightown, the acid 

 lava appears to occupy the same fissure as that tilled in one por- 

 tion by the basic lava. In this case the acid eruption may 

 represent an opening upon the same line of weakness at a 

 separate time, or it may occupy a fissure slightly divergent from 

 the basic fissure, the contents of each not coming into actual 

 contact. The exposures upon the ground are insufficient to 

 settle this question. Considerable variations of texture appear 

 in these acid rocks, but no system is to be observed in their 

 distribution other than a growing fineness toward the boundary 

 of each body. In their extremely weathered condition, as 

 shown by Mr. Darton, they easily escape observation and they 

 may possibly be more widely distributed than is now known. 



