OP ARGILLACEOUS SCHISTUS OR CLAY SLATE. 33 
sition rocks, agreeing in this one particular, that they are formed 
principally of the consolidated fragments and ruins of older for- 
mations, which will require a particular description. They pass 
into each other by insensible shades, and though in some cases 
it is easy, it is in others impossible to determine, by its minera- 
logical or natural-historical characters, to what divison a given 
specimen is to be referred. They are all included by McCulloch, 
under the single denomination of Argillaceous Schistus, of which 
he regards them as mere varieties. 
OF ARGILLACEOUS SCHISTUS OR CLAY SLATE. 
20. This substance affords a good illustration of the difficulty 
just stated, of separating the strata of the globe into well defined 
and distinct classes. It generally covers granite, gneiss, mica 
slate, and the other rocks that are unquestionably primitive; from 
which it is inferred that it is itself of more recent origin. But 
it also alternates, though in beds generally of inconsiderable thick- 
ness, with those substances, shewing that it had begun to be de- 
posited, whilst the causes that gave being to those rocks were 
still in operation. On the other hand, small beds of granite, gneiss, 
and mica slate, occur amongst strata that are made up of the frag- 
ments of older rocks, proving that the formation of rocks by the 
agency of chemical affinity did not suddenly and entirely cease 
when the mere mechanical aggregates began to be deposited. 
Under the single denomination of argillaceous schistus, Mc- 
Culloch includes, as has been stated, a number of substances un- 
like each other, and that have heretofore been treated as distinct 
species. They are generally mechanical aggregates. They differ 
in composition and the fineness of their constituent particles or 
fragments, but are so intimately associated and pass into each 
other by such insensible gradations, and at such moderate dis- 
tances, that it is thought they should be regarded only as forms 
of the same rock. A few of the more common and marked va- 
rieties will require a particular notice. 
Proper Jlrgillite or Clay Slate, is a common substance in 
North Carolina, where it generally exhibits a disposition to split 
by the aclion of the weather or of mechanical force into thin 
lamina?, though some varieties merely separate into tables which 
are without any indications of a schistose structure. It enters 
largely into the composition of the great transition formation that 
stretches through the central counties. The part of this forma- 
tion lying in Anson and Mecklenburg is made up almost exclu- 
sively of this rock. On the Pedee it is seen at Parker's ford 
about the South Carolina line, at the Grassy Islands, the mouth 
of Rocky river, and from the latter point, at intervals, as high as 
the mouth of Flat-swamp creek in Davidson. It abounds in 
Montgomery, Randolph, Moore, Chatham, Orange and Person. 
It is the lowest rock as we descend the Neuse, occurring about 
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