Page:VCH Lancaster 1.djvu/44

A HISTORY OF LANCASHIRE The lower zone lies in calcareous shales. Numerous other genera and species occur, amongst them being Rastrites peregrinus, Diplograptus Hughesii, Climacograptus normalis, etc. Crustacea are represented by trilobites such as Acidaspis, Prœtus, Harpes, Phacops, Encrinurus, etc.; brachiopods by Leptæna quinquecostata and Atrypa flexuosa; cephalopods by Orthoceras.

Dr. J. E. Marr, when discussing the general facies of these beds, drew attention to the fact that the dominant forms were almost all Silurian, and indicated a relation to the May Hill beds of Wales. A similar conclusion has been reached by other observers, and the beds together with the overlying Browgill or Pale Shales series are now classed as equivalents of the Llandovery Group.

The Browgill beds, which are frequently termed the Pale Shales, are very similar to certain beds associated with the Graptolitic Mudstones. They have a thickness of about 130 feet, and have yielded graptolites and brachiopods, examples of Monograptus lobiferus having been found in them on Applethwaite Common, and Stricklandinia lirata in the Pale Shales of Rebecca Hill near Ulverston.

CONISTON GRITS AND FLAGS

Coniston Flags.—The Coniston Flags, which have a great thickness and are well exposed in the Coldwell and Brathay quarries, about two miles south-west of Ambleside, consist of finely laminated blue flags, overlaid by three series of flaggy and calcareous grits. Dr. Marr divides them as follows:—

Brathay Flags.—The Brathay Flags are of fine texture, and cleave readily, and make up about a third of the total thickness. They are sparingly fossiliferous, and have yielded Favosites aspera, Monograptus priodon, Retiolites Geinitzianus, and a few other forms, chiefly in the neighbourhood of Stockdale.

The Coldwell Beds are made up of basal coarse grey grits, middle calcareous flaggy grits of a blue colour and fairly fossiliferous, and an upper series of blue to grey gritty flags, which exceed in thickness the middle and lower beds and Brathay Flags combined.

The Upper Coldwell beds are well seen in a quarry 200 yards south of the Coldwell quarry. The numerous fossils obtained from the Middle and Upper series include the corals, Petraia, and Favosites fibrosa; a trilobite, Phacops obtusicaudatus; brachiopods such as Orthis and Strophomena, cephalopoda, amongst which are six species of Orthoceras, and malacostraca; Ceratiocaris and Peltocaris being found in the upper beds at Troutbeck and Rebecca Hill. The Brathay Flags are of Wenlock Group age, whilst the Coldwell Beds correspond to the lower portion of the Lower Ludlow Group.

Coniston Grits.—These beds have a thickness of from 4,000 to 4,200 feet and consist of flags and felspathic grits. In the Sedbergh district they have yielded a suite of fossils which show them to be closely related to the Coniston Flags below, the grits and flags together corresponding to the whole of the Lower Ludlow Group of Shropshire and Wales.

BANNISDALE FLAGS

This series of beds, which attains a thickness of over 5,000 feet in the adjoining counties of Westmorland and Cumberland, consists of slates, grits and flags. Their representatives in the Lancashire area are to be found in the Upper Ireleth Slate group described by Sedgwick in 1846, who showed that they could be traced along the line of strike by Coniston Water and Windermere to Long Sleddale and Bannisdale Foot. The great slate quarries at Ireleth are opened in these rocks.

KIRKBY MOOR FLAGS

This group overlies the Bannisdale series beyond the Lancashire border on the north-east.

OLD RED SANDSTONE

Between the uppermost members of the Silurian in Lancashire which we have now dealt with, and the Carboniferous, there intervenes the Old Red Sandstone, a great deposit of red and grey sandstone, and flagstones, with conglomerates and shales. Although representatives of this system occur in adjacent counties, there is yet no evidence of its occurrence within the county beneath the Carboniferous Limestone. As, however, the Upper Old Red conglomerate underlies the Carboniferous Limestone in Cumberland, it is possible that if the base of the latter was exposed in Lancashire, we should also find the conglomerate beneath it. The conditions which existed in 4