OF SOUTH CAROLINA. 105 
of the altered rock ring like clink-stone. Above Liberty Hill dark gray masses of rock are seen on 
the surface and extending towards the river, and are all that remain to mark the course of an 
extensive dyke, now converted, by disintegration, into a fertile and productive soil. But the 
vicinity of Cambridge presents the most remarkable locality of trap rocks in the District. A cir- 
cuit of six or eight miles around this place is occupied by a series of trap and porphyritic dykes, 
yet so completely have the destructive atmospheric agencies done their silent work, that there is 
barely sufficient solid rock left upon the surface to indicate to the observer the geology of the 
region. 
Feldspar porphyry seems to intersect the trap, and near Fellowship Meeting-house the largest 
mass of the former rock is found; it may be seen on the road not far from the meeting-house, where 
it is converted, by decomposition, into a soft, pylverulent earth. 
From Cambridge trap may be traced at intervals, on the Martin Town road, and thence to Bea- 
verdam Creek. 
The person must be singularly unobservant who passes from the clay slate of this section of 
the District, without being struck with the difference presented by these formations. 
Metamorphic Rocks.—The influence of the underlying granite is seen in the highly inclined 
position of the gneiss and other rocks forming the ridge upon which the Court House stands.— 
South of the village gneiss is seen standing nearly vertical—strike N. 40° E. and south-west of 
this, and towards the Savannah, it is exposed, alternating with beds of feldspar and with horn- 
blende slates. Similar alternating beds are seen on the plantation of P. Brooks, Esq. where they 
are quite fissile and standing nearly vertical. From this they extend to Horn’s Creek; and at 
Longmier’s mill the hornblende slates of the series rise into prominent hills which extend beyond 
Martin Town to Gunner's Creek. 
Near the fork of Cedar and Horn’s Creek, and for miles around, hornblende is the prevailing 
rock. ‘The short and rounded hills and the broken character of this part of the District, is due to 
the destructible nature of this rock. The brown, warm soil derived from it presents a striking con- 
trast to the cold, gray soils of the clay slates through which Stevens’s Creek flows, nearly through- 
out its entire length. 
Mica, Talcose, and Clay Slates.—The geological relation of these rocks is well displayed 
between Hamburg and the Court House. About three miles above the former place, at the first 
falls of the Savannah, clay slates are found outcropping on the bank, in bold ledges—strike N. 20° 
E. dip S. E. 20°. Twelve miles north of Hamburg, and five miles from the river, the Tertiary 
terminates, and instead of the rounded pebbles and gravel of this formation, the surface is strewed 
with angular fragments of quartz. 
The occurrence of these fragments, and the rapidity with which they accumulate on cultivated 
land, are often puzzling to those unacquainted with their origin. The clay and other slates are 
often intersected by numerous quartz veins, which vary in thickness from many yards to a mere 
thread; and when they come to the surface they are broken down and scattered over it, in frag- 
ments of various sizes. being hard, and not readily acted upon by atmospheric agencies, they 
remain, while the more destructible slates are subject to disintegration and waste from rains and other 
causes. Every successive ploughing breaks and brings to the surface portions of these veins, and 
thus the accumulation proceeds until, in some instances, the surface is completely hidden. 
27 
