to Mr. Etheridge, the lower sandstones of the Foreland and the higher beds of Pickwell Down. They attain a thickness of about 1,500 feet, and extend from Croydon Hill to Trentishoe (=Trentishoe Beds). They contain few fossils.

ILFRACOMBE GROUP.

Combe Martin Limestone.

Above the Hangman Grits is a series of calcareous silvery shales or slates with bands of limestone, containing Stringocephalus Burtini (=Stringocephalus limestone'), and Streptorhynchus, Cyathophyllum, &c., extending in a band from near Withycombe to Ilfracombe and Lee Bay, and attaining a thickness of about 4,000 feet. The limestone beds of the Quantocks belong to this series.

The bands of limestone form a small proportion of the series, but they are in many places worked for lime. In some places, as at Kentisbury, contemporaneous Igneous rocks have been noticed by Mr. Etheridge; the beds are worked for road-metal.

MORTE SLATES (MORTEHOE GROUP).

This series comprises the pale grey and purple unfossiliferous glossy slates of Challacombe and Mortehoe, having a thickness estimated at from 3,000 to 4,000 feet.

They extend from the Oakhampton Slate Quarry, near Wiveliscombe, to Mortehoe: they contain no recognised limestone bands. The valuable spathose iron-ore of the Brendon Hills occurs in these beds.

The slaty beds of Hestercombe may perhaps be on this horizon, as also those of Lundy Island.

UPPER DEVONIAN.

PICKWELL DOWN SANDSTONES.

Woolacombe Sandstone.

These consist of red micaceous sandstones, shales, and conglomerates. They extend from Pickwell Down to near Wiveliscombe, and partake much of the character of Old Red Sandstone. They are about 3,000 feet in thickness, and contain hæmatite.

BAGGY AND MARWOOD SLATES (CUCULLEA ZONE).

These consist of a series of slates and sandstones characterized by Cucullaa (C. trapezium), and extending from Baggy Point to Marwood, and according to Mr. Etheridge as far as Dulverton.

In the sandstones of Sloly Quarry, Lepidodendron and Calamites are found. Mr. Salter identified the Marwood Beds with the Upper Old Red Sandstone.

The Pilton Group consists of a series of calcareous sandstones, grey shales and slates, and nodular bands of limestone, containing Strophalosia caperata, Spirifer Barumensis, Phacops latifrons, Bellerophon, Aviculo-pecten, Encrinites.

Top Orchard Quarry is a well-known locality for the fossils. This group includes the Beds of Croydon, Braunton, Pilton, and Barnstaple: south of the last-mentioned town, the beds pass gradually into the Culm-measure Series. (See p. 106.)

RELATIONS OF OLD RED SANDSTONE AND DEVONIAN.

In attempting to parallel the Devonian strata with equivalent beds in other parts of the country, the first inquiry is naturally concerning the relations between them and the overlying true Carboniferous rocks. This relation is not quite clear in South Devon, owing to disturbances; but, in North Devon, the beds pass gradually one into the other. Now these Carboniferous rocks are generally classed with the Millstone Grit and Coal Measures, but there are several calcareous bands at the junction of the Culm-measures and Devonian strata, which have been regarded as partly representing the Mountain Limestone.

In South Wales, about Haverfordwest, the Carboniferous Limestone has become much attenuated; while in Ireland the Limestone becomes in certain localities replaced by the Carboniferous slate which generally underlies it. When we trace the Carboniferous limestone northwards beyond Derbyshire, the calcareous element becomes less, and the series consists of bands of limestone intercalated with shales and sandstones, and containing seams of coal.

Looking at these changes, it seems only reasonable to consider that at least some of the upper portions of the Devonian series may be paralleled with the Lower Carboniferous strata of other districts.

It is admitted on all sides that the lowermost Devonian strata are identical in character with beds of Old Red Sandstone: it would seem, therefore, that the boundary-line between the Old Red Sandstone and Carboniferous systems must be drawn somewhere between the Upper and Lower Devonian strata. Such a line, however, may never be fixed with precision. The Devonian area exhibits, on the whole, a more uniform series of conditions than we find in other

If we

districts to have characterized the same period. regard the Old Red Sandstone as entirely formed in fresh waters, we require a considerable barrier to separate the purely marine area of the Devonian slates and limestones from the lacustrine sands of the Old Red period; and such a barrier (if it ever existed) must be drawn somewhere between the Mendip and Quantock Hills, and there is no physical evidence to support it.

Any one who examines the limestones of Torquay, Newton, and those of the Mendip Hills and South Wales, cannot fail to be struck with the general identity of their lithological characters: at the same time it is clear that the fossil contents are on the whole different.

Nowhere do we find the Devonian strata immediately overlying the uppermost Silurian rocks, and nowhere is there exhibited any horizontal passage of the Old Red Sandstone into slates of the Devonian type. There is no base to the Devonian series, and Sedgwick admitted it to be the safest plan to place the Cornstone group below all the groups of Devonshire.1

Mr. Jukes regarded the red sandstones of the northern portion of the Quantock Hills, those of Dunster, Minehead, and Porlock, as of Old Red Sandstone age. The overlying slates of Lynton, Ilfracombe, &c., he identified with the Carboniferous slate; while the sandstones of Pickwell Down, Haddon Down, and Main Down, he regarded as probably a repetition of Old Red Sandstone brought up by a concealed fault; and he considered that the overlying slates of Marwood, Braunton, and Pilton again represented the Carboniferous slate which passed gradually upwards into the Culm

measures.

Mr. Jukes thus paralleled the groups on either side of the fault:

1 Brit. Pal. Rocks, p. xxiv.

The slaty rocks and associated limestones of South Devon and Cornwall are so much broken up and disturbed, compared to the equivalent beds in North Devon, that no very accurate parallels have been made.

Large masses of granite and many other rocks of igneous origin, intersect or protrude through the killas' or clayslate of Cornwall and Devon.

The Limestones of Plymouth (Plymouth rag), Chudleigh, Ashburton, Ipplepen, Berry Pomeroy, Torquay, St. Mary Church, and Newton Abbot (the Great Devon Limestones) are as well known from their purely economic value for marble, building- and paving-stone, as some bands of the rock are from the richness of their palæontological contents. The numerous remains of corals render the rock, when polished, very beautiful: it is called Madrepore marble. These corals belong to the species Heliolites porosa, Favosites polymorpha, Cyathophyllum cœspitosum, Astræa pentagona, &c. Among the Mollusca, Orthoceras, Clymenia, Goniatites, Loxonema, Murchisonia, Rhynchonella, Spirifera, Stringocephalus Burtini, &c. are found.

Trilobites likewise are met with, as Phacops latifrons, Bronteus flabellifer, &c.

Mr. Etheridge places these limestones on the horizon of the calcareous beds of Ilfracombe. They appear to form the highest beds of the South Devon strata, being connected,

1 It is considered that the masses of annulated chalcedony, called Beekite, found in the neighbourhood of Torquay, are Devonian corals more or less completely replaced by silica, for they are sometimes hollow, and in other instances contain a nucleus of fossil coral.