on the Geological Survey of South Carolina. 63 



western section of this state, and this rock composes a considera- 

 ble portion of the surface of some districts. Generally this, with 

 the associated rocks, have become so much disintegrated as to 

 make the boundary of the dikes obscure ; and our author states 



that he did not meet with a Single instance where anything like 



an escarpment was presented. The direction of the dikes is 

 uniformly between 15° and 35° east of north, and they are rare- 

 ly inclined much from the vertical. 



In Chester district the trap is more developed than elsewhere, 

 covering over a large portion of its surface, and veins of por- 



phyritic feldspar, quartz and graphic granite, intersect it. 









The dikes of intrusive rock are not all trap throughout this 

 region. Some are of syenite, others of hornblende rock and of 

 eurite. One of the syenitic veins in York district is intersected 

 by veins of quartz which have been worked for gold. Evidence 

 of the igneous nature of all these rocks is seen in various locali- 

 ties. By their junction with the clay slates of Edgefield, the 

 latter are changed to porphyry, and in Chesterfield the new red 

 sandstone is blackened and otherwise altered, so as to resemble 

 overburnt brick. 



In Abbeville district, at a locality on Little river, the trap pre- 

 sents a remarkable structure on its surface, being divided by 

 concentric joints, which are crossed by others nearly coincident 



with the radii of the curves. This is illustrated by a cut as 

 follows : 



The trap rocks of the state have not been found to contain 

 any minerals of interest. 



Stratified metamorphic rocks. — Gneiss. — The non-fossilif- 

 erous series of stratified rocks present themselves at the surface 



neiss is 



over a large portion of the primary region, and of these 



|jy far the best developed. Of the prevalence of this rock Mr. 



Auomey remarks, that " although its continuity is often inter- 

 ru pted b Y the protrusion of the underlying granite, or the alterna- 



jon of beds of other rock, and may be covered by patches of 

 Jne overlying slates, yet it is seen forming a vast plain that ex- 

 tends from the mountains to the middle of the state, forming, 

 ^th a few exceptions, all the obstructions to the rivers. The 

 stnke being at right angles with the courses of the streams that 



rain tlle Atlantic slope, a series of falls is produced by the out- 



