OF ARGILLACEOUS SCHISTUS OR CLAY SLATE. 
33 
sUion rocks, ngrcclng; in tliis one particular, tliat they are formed 
principally of the consolidated fragments and ruins of older for¬ 
mations, which will reejuire a particular description. 'J'hey pass 
into each other by insensible shades, and though in some cases 
it is easy, it is in otliers impossible to determine, by its minera- 
logical or natural-historical characters, to what divison a giyen 
specimen is to he referi'cd. They are all included by jNlcCulloch, 
under the single denomination of Argillaceous ScliisLus, of which 
he regards them as mere yarieties. 
OF ARGILI-ACEOUS SCIIISTUS OR CLAY SLATE. 
20. This substance affords a good illustration of the difficulty 
just stated, of separating tlie strata of the globe into well delined 
and distinct classes. It generally coro'S granite, gneiss, mica 
slate, and the otlier rocks that ore uncpiestionably primitiye; from 
^yhich it is inferred that it is itself of more recent origin. I5ut 
it also alternates, tliough in beds generally of inconsiderable thick¬ 
ness, with those substances, shewing that it had begun to be de¬ 
posited, whilst the causes that gaye being to those rocks were 
still in ojicration. 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. 
L’nder the single denomination of argillaceous schistus, ]\[c- 
Culloch includes, as has been slated, a number of substances un¬ 
like each other, and that have heretofore been treated as distinct 
species. 'I'hey are generally mechanical aggregates. They ditl'er 
in composition and the fineness of their constituent particles or 
fragments, but are so intimately associated and jiass into each 
other l.'y such insensible gradations, and at such model ate dis¬ 
tances, that it is thought they should be regarded only as forms 
of tbe same rock. A few of the more common and marked va¬ 
rieties will require a particular notice. 
Proper ^.QrgHiite or CUnj Slate, is a common substance in 
Noith Carolina, where it generally exhibits a disposition to sjdit 
by the action of the weather or of mechanical force into thin 
lamiine, though some varieties merely separate into tables which 
are without any indications of a .“chistose structure. It enters 
largely into the composition of the great transition formation that 
stretches through the central counties. The part of this forma¬ 
tion lyii’g in Anson and Mecklenburg is made up almost exclu¬ 
sively of this rock. On the Pedec it is seen at Parker’s ford 
about the South Carolina line, at tlie 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 Jscuse, occurring about 
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