[From Mannin vol 1, 1913]
The story of the search after coal and of the discovery of the salt-field in the north of the Isle of Mann, is worthy of being told because it not only adds a new interest to our beautiful Island, but also illustrates the inductive methodsor the principles of common senseby which Geology has become a science.
The geological structure of the Isle of Mann, first made out in its main outlines by Cumming in 1848, and afterwards elaborated by various workers, is now known in considerable detail. It is as follows
1. The Slates and Quartzites that form the greater part of the Island are of great thickness, and are locally folded and traversed by great lines of smash or faults. They are also riddled by volcanic dykes, and penetrated by masses of igneous rock, such as that at Poortown and north of Wills Strand, near Peel, and by bosses of granite as at Foxdale, the Dhoon, and Santon. They form the lofty cliffs that characterise the greater portion of the coastline, and are the rocks out of which Snaefell and all the rest of the higher hills have been carved by rain, rivers, ice and snow, during the immeasurable past. They originated as mudbanks and sandbanks in the sea, and were hardened into their present state by pressure, earth-heat, and the injection into their mass of igneous rocks, lavas, and granites at various times. They constitute the Ordovicean, or Lower Silurian strata in geological classification.
To the south, in the neighbourhood of Castletown and Port St. Mary, the Ordovicean rocks are covered by the thin red sandstones and conglomerates, constituting the beautiful natural arches of Langness, and passing on the foreshore under the thin limestones of Castletown Bay, and the coastline of Derbyhaven as far north as Cass ny Awin. At Scarlett Point and Poolvaaish they are interbedded with volcanic ash, and traversed by dykes, and necks of lava, proving that the sea-bottom in which the calcareous mud (now limestone) was being accumulated was disturbed by volcanic eruptions. The red sandstones and the limestones constitute the two lower beds of the Carboniferous age. They have been inlaid into the Ordovicean rocks by the great Port St. Mary fault running from Perwick Bay through Arbory to Balla Kewin. In this way a fragment of the Lower Carboniferous ring, once surrounding the Ordovicean, has been preserved to constitute the low rounded hills of the south of the Island, and the lovely valley of the Silverburn north of Castletown.
If we now examine the north of the Island, and take the points of view offered by the battlements of Peel Castle, we see to the south the lofty cliffs of Thistle Head, formed of the folded slaty rocks, contrasting with the bright red rocks on the north-east of Creg Maim and the Stacks, dipping seaward. The grey slates of St. Patricks Isle and of Peel Hill abruptly end, on the west side of the harbour, in clays, sands and gravels, on which the city stands, and extending irregularly over the red rocks on the north-east. These red rocks some 1707 feet thick are of Permian age, and contain pebbles of carboniferous and other rocks, like those which cover the coalfields of Lancashire, Yorkshire and Cumberland. They also, like the lower carboniferous rocks of Castletown, have been inlaid into the slates by the faults that can be seen on the foreshore near the Creg-Malin quarry and in Wills Strand. Here black and grey decomposed slates reappear, and form the greater part of the cliffs, in the direction of Kirk Michael, until they pass under the water-line, and are concealed by the clays, sands and gravels of glacial age, covering the greater part of the Island, and constituting the whole of the lower ground, north of a line passing from Ballaugh to Ramsey at the base of the steep hills of slate. These hills undoubtedly mark an ancient coastline, the ancient cliffs being in ruins, and mostly carried away by subaerial action and more especially by the erosion of streams and the friction of glaciers, by which they have been moulded to their shapes.
The contrast between the hills culminating in Snaefell, and the northern plain, forced upon me while engaged on my geological map of the Island, is so marked that I was led to enquire whether other rocks similar to that surrounding the slaty centre of the Lake District, Carboniferous, Permian, and Triassic, were not concealed beneath the superficial deposits forming the northern plain. Also it was probable that the coal measures that plunge beneath the sea at Whitehaven, might occur somewhere between the Point of Ayre and the hills to the south.
It was under these circumstances that Messrs. Craine, of Liverpool, under my advice made a series of borings 1891-8, Mr. Todd, the present manager of the Salt Works being in charge. These revealed the true structure of the rocky floor below the northern plain. In the first, at Lhen Mooar, on the western coast line, the carboniferous limestone was met with at a depth of 167 ft. 6 ins, below the surface, dipping at a high angle to the north. In the second, at Ballawhane, about 1430 yards along the coast further to the north the strata are:
Glacial sand, gravel and boulderclays 171 ft.
Triassic sandstone . . -- . -373
Yoredale shales and sandstones...136 ,,
Carboniferous limestone .....12 ,,
The third at Knock-e-Dooney about 1536 yards from Ballawhane to the north east, showed in addition to the above strata the Permian rocks of the Peel cliffs.
Glacial drift as before- . -...173 ft.
Triassic sandstones. -.. - -432 ,,
Permian strata - -.- -.29,,
Yoredale shales and sandstones ... 283
Carboniferous limestone .... . -15 ,,
The fourth at Ballaghenny about 3630 yards further to the north-east, gave a somewhat similar section.
Glacial drift as before- - -212 ft.
Triassic sandstone 743
Permian strata ~.. 84,,
Yoredale shales and sandstones- . -240,,
The fifth boring at the Point of Ayre close to the Lighthouse a little over two miles from the last gave the following results
Glacial drift as before- -. 198 ft.
Triassic marls with salt and gypsum 680,,
The sixth and last, some 400 yards away to the south-east, repeated with slight modifications the same section.
Glacial drift as before. 343 ft.
Triassic marls with salt and gypsum 557 ft.
In all these borings the limestones and Yoredales dipping at a high angle are covered by the Permians and Triassic strata, dipping northwards at lower angles. They occur in their natural order, the limestones in the south, then the Yoredales, and extending northwards as far as Ballaghenny. Then the Permians and the Triassic sandstones and the salt bearing marls. It was therefore likely that the coal measures would be struck in their natural position further to the north. To ascertain this the borehole No. 5 at the Point of Ayre was deepened, partly at the expense of the Crown, to 1980 ft. below the surface, at which point the exploration was stopped, the bottom of the borehole being in the Peel sandstones, and the Triassic sandstones above occupying their natural section below the mans. It is most unfortunate that the borehole was not continued to the base of these sandstones, which would have settled the question of the range of Whitehaven Coalfield under the sea into the north of the Island. If it is present, it is at a depth of about 3000 ft. below the surface, too deep to be worked to a commercial success.
We may note that several other efforts have been made to discover coal in the Island, in the south in the dark carboniferous shales of the Silverburn; in the north in the black decomposed Ordovicean Slates of Wills Strand and in the same rocks near Glen Faba Bridge, Peel, by Messrs Corrin and Morrison. All were in rocks older than the coal-measures, and were carried out before the rocks of this Island had been mapped. Now we know that the only place where coal measures can occur in the Island is the Point of Ayre.
If, however, coal be left out of account, the unexpected discovery of salt is a most important asset, because it has led to the establishment of a new industry in the Island. The total thickness of the rock salt in various beds, is about 100 feet, and there is also a flow of brine of considerable but unknown magnitude. This is pumped at the Point of Ayre, and conveyed in a pipe to Ramsey by the Manx Salt and Alkali Company, established by Messrs. Craine in 1901. Here it is manufactured into salt, chiefly used for preserving fish. It is, in my opinion, the beginning of an industry in the Island that will give employment to many workers, as well as yield adequate profits to the company. Messrs. Craine have deserved well of the Manx people for having taken up the views of the writer of this article, and having persevered in testing their truth at considerable cost, with the result of adding a new industry to the Island.