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in the Trilobite slates of Exmoor (No. 7) render them too insignifi- 
cant to be noticed ; that the Posidonia limestones, which by mineral 
gradation succeed and conformably overlie the latter, are elliptically 
included in the Coddon Hill grits (No. 8), and together distinctly 
underlie and constitute the base of the great floriferous series (No. 9) : 
that higher up in No. 9 is an extended horizon, which separates the 
series into an upper and a lower, containing the Bampton, Hock- 
worthy, Holcomb Rogus, and Hastleigh limestones, with red and 
black slates on the north; the Petherwen and Landlake slates and 
limestones on the south; and the entire suite of coral limestones to 
the east of Dartmoor, extending from Chudleigh to Berry Head 
and Brixham: that the Plymouth limestones included in the killas 
(No. 10) are higher in the group than those just mentioned, and 
are introduced first at Millaton, about a mile and a half west of St. 
Germains. 
Mr. Williams considers the slate or killas series of S. Devon to be 
distinguished from the slates of Exmoor by a peculiar extraneous 
cleavage. In Exmoor the cleavage, he says, is at all angles, from 
less than 10° to the vertical, its planes having a direction of about 
east and west ; whilst the cleavage lines of the killas either coincide 
with the magnetic or true meridian, or depart from it to the east or 
west only a few degrees, and the inclination approaches the vertical 
with a strike N. and S., or nearly perpendicular to that of Exmoor. 
What, says Mr. Williams, are the results, if the question be tested 
by the assumed law, that strata may be identified by their organic 
remains? If the Posidoniz and Gonitatites of the lenticular, black 
limestones, never exceeding thirty-five feet in thickness, be appealed 
to, to identify them with the mountain limestone, the weight of 
organic remains opposed to them in the Launceston and Petherwen 
fossils, the corals and other organic remains of South Devon belong- 
ing to the floriferous series, reduces the evidence to dust. If mineral 
characters be appealed to, he says, they fail altogether. 
In conclusion, Mr. Williams remarks that in this supplement, he 
has endeavoured faithfully to transfer the simple truths of nature to 
his pages, without reference to the theories of others. He would, 
however, remind geologists that the proposed law of Mr. W. Smith, 
is no law, if it do not imply a final and universal extinction of 
species. This being his own view, Mr. Williams says, he could not 
admit that the Gonitatites and Posidoniz of Devonshire were first 
introduced and became extinct with the mountain limestone, being 
justified by the fact of superposition, and more reasonable analogy, 
in concluding that these genera existed elsewhere in congenial con- 
ditions during the entire period of the deposition of the Trilobite 
slates, when that formation ceasing in Devonshire, the ova of the 
creatures or the creatures themselves were transported to a region 
favourable to their existence, and were continued during epochs of 
duration up to the period of the mountain limestone, and probably 
beyond it, if they be not now in existence. They appear, in his 
opinion, like the corals of Devon, to have been subject to repeated 
mineral accidents, and to have been locally destroyed in groups, 
