INTRODUCTION. XL 
forms of limestone,—in both of which places it has yielded me specimens of the above- 
named shells. Probably the brecciated beds at the north end of Black Hall Rocks, like 
those at Tynemouth Cliff, are partly formed of the débris of the fossiliferous limestone, 
true beds of which are seen, at little more than a mile distance, in Castle-Eden-Dene. 
The conditions under which the Permian Rocks of the North of England have 
been formed, are worthy of investigation. The lowest member of the series, the 
freestone (/), like arenaceous deposits in general, appears to have been accumulated 
in shallow water: this view is to a certain extent proved by the presence of land 
plants in some of its beds, as at Westoe; and by the surface of other beds being in 
some places (Thrislington Gap) crowded with strong ripple marks. In some localities, 
as at Tynemouth, it appears to have been accumulated in a violently agitated sea,— 
perhaps on a coast margin,—some of its beds containing large angular fragments 
of a purple-coloured sandstone, and having quite the character of a conglomerate. 
The Marl-slate (e) is apparently another shallow water or littoral deposit; as it 
contains, in addition to A/ye, the remains of Ferns (ewropteris Huttoniana) at 'Thickley, 
and Thrislington Gap. The fishes, with which it is everywhere loaded, also attest 
its littoral origin; as the genera which characterise it, namely, Paleoniscus, Pygopterus, 
Celacanthus, and Platysomus, from their abundance in certain Coal-measure deposits, those 
of Yorkshire in particular, may be safely concluded to have lived at no great distance 
from the shore. The presence in the Thuringian equivalent of the English Marl-slate 
of Lingula Credneri, Discina speluncaria, Productus horridus, Camarophoria Schlotheim, 
Pleurophorus costatus, Bakevellia antiqua, Kenestella retiformis, and probably some other 
species, #f they were generally numerous, might be considered as strongly opposing this 
conclusion. The next member of the system,—Compact limestone (/), concluding from 
its mineralogical and chemical characters, and from the fragile nature of many of its 
organic remains (Acanthocladias, Strophalosias, &c., Whitley), appears to be a pelagic 
deposit. The same conclusion may be safely advanced with respect to the overlying 
member, the Fossiliferous limestone (c); for it is impossible to conceive, that such 
delicate organisms, as the numerous Ciliobrachiate Corals, and spiney Palliobranchs 
imbedded in it, could have existed any where except in deep water. In nearly all the 
localities where this limestone is seen, it has a very irregular structure, and scarcely 
offers any appearance of stratification: it is clearly a chemical deposit; and from the 
circumstances noticed, I am strongly disposed to regard it as having been formed, or 
rather precipitated, in a very rapid manner. The brecciated member (4) has evidently 
been deposited under unusual circumstances: it nowhere contains fragments of any 
other than Permian limestone; but the size of these fragments, measuring, in some 
localities, two feet in diameter (Tynemouth Cliff), and weighing, in others, several tons 
(Ryhope), indicates, however contiguous the parent bed from which they were torn 
may have been, that they were heaped together by powerful cataclysmal agencies. 
The next and last member of the series, the Crystalline member (a), possesses, in its 
often finely laminated character, that is, when observed in its normal or unaltered 
