As at present constituted, the Island, with the detached islet of The Calf off its south-western extremity, contains 227 square miles (140,325 acres), of which 170 square miles, or three-fourths of the whole, are occupied by the slate and greywacke rocks, probably of Upper Cambrian age, composing the hilly massif. Strata. of the Lower Carboniferous age occur in a small basin of 7 or 8 square miles at a low elevation in the South of the Island, and a narrow strip of red sandstone, probably belonging to the same period, borders the coast for two miles about midway upon the western side. The northern extremity consists of a low-lying tract of about 45 square miles, which is an addition made to the Island in glacial times by the deposition of great masses of glacial drift upon the pre-glacial sea-floor. Deep borings through this drift have recently revealed a rock-floor of Triassic, Permian, and Lower Carboniferous strata at a considerable depth below sea-level.
The position of the Island as regards the neighbouring shores. Its northernmost point is 16 miles distant from the nearest headland of the Scottish coast, while its closest approach to the Cumberland shore is 31 miles, to that of Ireland in Co. Down 31 miles, and to the Welsh coast near Holyhead 45 miles. The same map shows roughly the contours of the surrounding sea-bottom. To the eastward of the Island the depth is nowhere more than 20 fathoms, to the north ward it rarely reaches 30 fathoms, to the southward it usually ranges between 30 and 50 fathoms, while to the westward midway to the Irish coast there is a long narrow trough descending to over 70 fathoms.
Rising from the middle of the Irish Sea, within sight of each of the three Kingdoms, with a history and associations so distinct, yet so intimately linked with those of' the rest of Britain, this interesting Island presents in its geological structure features that connect it alike with England, Scotland and Ireland, while at the same time it retains a marled individuality in regard to some of the rocks that form its framework." These words, with which Sir Arch. Geikie preludes his account of the volcanic rocks of the Isle of Man serve equally well as an introduction to its general geology.
The predominant feature in its stratigraphy is the central ridge of slate and greywacke, which seems to have constituted an insulated tract at as early a date as the beginning of the Carboniferous Period. This prototype of the present Island appears afterwards to have been enfolded and obliterated by the sediments of later times; but with the progress of denudation the old ridge has once more emerged from beneath this mantle. Its insular character is as well maintained in its physical as in its geological features. The erosive agency of the simple drainage system, descending radially to the sea from the central hill-ridge, together with that of the waves which surround it, is adequate to explain all the contours of its present surface. It must indeed frequently during its history have been reunited to the mainland by a continuous land surface; but at such times it probably still retained in some degree its characteristic individuality, and arose above the surrounding plain as a hilly tract with a self-contained drainage, although its streams may then have been tributary to a larger river-system lying beyond its limits.
The Manx Mines in 1246 of the island was at that time still under the dominance of Norway; and its King, Harald II, granted a charter by which the monks of Furness Abbey obtained the right to work the mines. In Chaloner's ' Caledonia ' (vol. iii., p. 372) that John Comyn, Earl of Buchan, obtained from Edward I. a license to dig for lead in the Calf of Man to cover eight towers of his Castle of Cruggleton in Galloway. In the course of the 15th, 16th, and 17th centuries, the noble family of Stanley appear to have sought for copper in the same neighbourhood; traces of their labours remain. The ore discovered, though not abundant, was rich in quality producing six pennyweights of copper per ounce of ore." In 1406 "mines of lead and iron" were included in the grant of the Island to Sir John Stanley by Henry IV.; and in 1422 it was ordered that the lord's mine should be managed by his " Lieutenant, Receiver, and Comptroller," who had to see that the miners did their duty. These were at Laxey, Foxdale, and ' Breda' Head; and he mentions also deserted shafts of lead-mines with rubbish-heaps between Port Erin and Kirk Arbory, no doubt referring to those since reworked as the Ballacorkish or Rushen mines. The third and fourth decades of the 19th century marked a. great revival and development of the Manx mining industry After that time its steady progress may to some extent be traced in the Mining Statistics published.
As at present constituted, the Island, with the detached islet of the Calf off its south-western extremity, contains 227 sq. miles (145,325 acres), of which 170 sq. miles, or three-fourths of the whole, are occupied by the slate and greywacke rocks, probably of Upper Cambrian age, composing the hilly massif. Strata of the lower Carboniferous age occur in a small basin of 7 or 8 sq. miles at a low elevation in the south of the Island; and a narrow strip of red sandstone, probably belonging to the same period, borders the coast for two miles about midway upon the western side. The northern extremity consists of a low-lying tract of about 45 sq. miles, which is an addition made to the Island in Glacial times time by deposition of great masses of Glacial Drift upon the Preglacial sea-floor. Deep borings through this drift have recently revealed a rock-floor of Triassic, Permian and Lower Carboniferous strata at a considerable depth below sea-level.
The position of the Island as regards the neighbouring shores. Its northernmost point is 16 miles distant from the nearest headland of the Scottish coast, while its closest approach to the Cumberland shore is 31 miles, to that of Ireland, in Co. Down, 31 miles, and to the Welsh coast near Holyhead 45 miles. The Island is irregularly oblong in shape, with its longer axis running N.N.E. to S. S.W., which is the direction of strike of the slate-rocks. In this direction, from the Point of Ayre to Spanish Head the land has a length of 30 miles, while the breadth of its wider central portion varies from 8 to 12 miles. Excepting in the well-cultivated northern plain, there is little flat ground. In the interior the physical features bear much resemblance to the Southern Uplands of Scotland. The hills are steep, but not generally craggy, and are arranged in long grassy or heather coverered ridges running with the longer axis of the Island, with broad intervening valleys. The highest of these ridges commences in the vicinity of the eastern coast near Ramsey, and is practically continuous to the south-western coast north of Port Erin, but is broken across in one place by a deep transverse valley, which intersects the Island between Peel and Douglas.
Most of the larger streams of the Island rise in the vicinity of Snaefell and fall outward in different directions to the sea, the Sulby River and Glen Auldyn water draining northward, the Cornah and the Laxey Rivers eastward, the Glass and the Baldwin south-eastward, and the Neb south-westward. The drainage of the smaller tract south of the transverse valley is radial from a separate centre in the south western portion of the hill-chain, whence flow the Glen Rushen waters north and northwestward, the Foxdale River northward, and the Santon, the Silverburn, and the Colby southward.