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A HISTORY OF LANCASHIRE

sequence and stratigraphical position has proved a most difficult one. At one time they extended much farther to the south-west, as a great part of the northern portion of the Isle of Man is made up of them. The Skiddaw Slates are, as a rule, unfossiliferous, although some of the less altered beds have yielded a fauna sufficiently distinctive to determine their true position. The most abundant organic remains are those of graptolites, of which 59 species are known. Other forms are brachiopods, such as Lingula brevis, genera of trilobites belonging to Æglina, Agnostus, and Asaphus, small crustaceans known as Caryocaris, and doubtful remains of plants. Miss G. L. Elles, who has made a special study of the Skiddaw Slates,^[1] is of opinion that the fauna is in the main of Arenig age, but that certain of the beds belong to lower and higher horizons.

BORROWDALE VOLCANIC SERIES

Towards the close of the Skiddaw Slate period the Lake District became a centre of great volcanic activity, showers of ashes and streams of lava being thrown out intermittently, and alternating for a while with the sediments then forming on the sea floor. Eventually the only accumulations taking place were those derived from the volcanoes, one or more of the latter rising above the sea-level into enormous mountains. The total thickness of lavas and ashes has been estimated at about 12,000 feet. They overspread a great portion of the Lake District, which owes most of its wild, rugged and mountainous character to them.

The Borrowdale Volcanic Series crosses the Lancashire border on its north-western side, and occupies a north-east and south-west strip of ground some sixteen miles in length and four miles in breadth at the widest point, lying between the boundary and a line drawn from the northern end of Lake Windermere to Broughton-in-Furness. This area presents all the characteristic features of the Lake District, and is very mountainous, the chief elevations being Dunnerdale, Coniston Old Man and Grey Friars. Most of the earlier lavas poured out during the Borrowdale Volcanic period were andesitic in character, whilst towards the close they assumed the condition of rhyolitic felsites. Many of the fine ash beds have undergone cleavage, and are now quarried for roofing slates. Near Coniston, ores of copper and iron occur in the beds, and mining of the former was carried on for many years.

THE CONISTON LIMESTONE SERIES

This series represents the upper limit of the Ordovician in North Lancashire, and has been classified by Dr. J. E. Marr as follows:—

		Ashgill Group $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Ashgill Shales, 50 feet. Staurocephalus Limestone, 5 feet.
Coniston Limestone Series	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Sleddale Group $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Applethwaite Beds, 100 feet. Conglomerate, 10 feet. Stile End Beds, 50 feet. with Yarlside Rhyolites above.
		Roman Fell Group	Corona Beds, 100 feet.

The series is generally accepted as the equivalent of a part of the Bala Beds of Wales, the remaining part of the Bala Beds and the Llandeilo being represented by the Borrowdale Series, whilst the Skiddaw Slates are, without doubt, in part of Arenig age, and may also in part correspond to the Tremadoc Slates and Lingula Flags.

On the Lancashire border, the Coniston Limestone Series does not seem to attain a greater thickness than 300 to 500 feet, and only the upper members are represented, namely, the Applethwaite Beds, Staurocephalus Limestone, and Ashgill Shales.

The Applethwaite series consists of very fossiliferous calcareous shales and limestones, with a white horny limestone at the top of the series, which in Dr. Marr's opinion is the equivalent of the Keisley Limestone. At Ireleth the beds rest on the Borrowdale rocks, whilst they can also be traced from the mouth of the Duddon northwards to near Ambleside. Good exposures of the Coniston Limestone Series are seen near Sunny Brow on the west of Windermere, and on the high moorland to the south-west of Coniston Water, the Applethwaite beds being especially fossiliferous. Dr. Marr, who has given considerable attention to these beds, states that the best section of the lower part of the series is shown at High Pike Haw, near the head of Appletreeworth Beck, whilst the upper portion is excellently displayed in Ashgill Quarry.

The Ashgill Shales.—These consist of grey and green calcareous shales with limestone, and have a variable thickness. They are well developed at Ashgill; at Rebecca Hill quarry, north of Dalton in Furness; near Coniston, and at various places in Westmorland.

1. Quart. Journ. Geol. Soc. liv. 463 (1898).

2