Chapter 2: Description of Loch Coirib

• Geography of Loch Coirib
  
• Sources, Rivers and Turlochs
  
• Scenery and Mountains Surrounding the Lake
  
• Geology
  
• Bogs and Turf
  
• Navigation
  

The lake naturally divides itself into four portions: the upper or Conamara and Joyce Country portion, from Mám to Dún, placid, and untenanted by islands, save the bare rock on which the ancient Hen's Castle of the O Conors and O Flahertys stands; the narrow portion along Dubhros and Ceann Eibhir; the broad "old lake," crowded with islands, that forms its middle portion the rocky narrow gut that commences below Inis Uí Chuinn, and, turning to the south, by the ferry of Cnoc and Coill Beag landing, opens opposite Port Darach, into the broad expanse of the free lower lake that forms its fourth part, and sends its volume of waters through the Coirib and Mionloch Rivers, and the "Friars' Cut," into the Gaillimh, and through it to the ocean, at the estimated quantity of one hundred and twenty-six thousand cubic feet per minute in summer. In the deeper parts the bottom is mud, and in the shallow ones gravel and rock.

The great carboniferous mountain limestone formation occupies all the eastern and southern shores, and the lower portion of the western, in a line drawn from Oughterard to Cong, occasionally cropping to the surface, and forming stratified fields of smooth bare rock, or where it meets the water being honey-combed like a colander and in other places grooved by the action of water, ice or the attrition of harder bodies passing over it, generally in a S.E. direction.

The geology of the upper lake is of a totally different character. "At Oughterard," writes Mr. Kinahan, "the limestone becomes inter-stratified with sandstone; and immediately north of that village is replaced by granite, which at Glan gives place to fossiliferous Silurian rocks, that lie uncomfortably on older gneiss, schist, quartz rock and primary limestone, with dykes and masses of vario igneous rocks. On the north of the lake the geology is similar, fossiliferous Silurian rocks occurring at the north west end of the Mám valley and extending by Kilbride and Loch Mask to Ben Levi and Cong, under which, bounding Loch Corrib, are found gneiss, schist, and primary limestone; and, extending from Ben Levi Lodge on Loch Mask to Cong, the mountain limestone is found capping the primary rocks. In the small eastern tract between the River of Cong and the stream at Cross, a detailed list gives an epitome of nearly all the rocks entering into the structure of the district about Loch Corrib: carboniferous limestone, yellow sandstone and fossiliferous Silurian grits and shales in sandstone, and a variety of whinstone similar to Cotta's description of diallage rock.

"In the townland of Gortachurra there are carboniferous limestone, conglomerates, and diallage rock- and in that of Ballymagibbon South, and the islands adjoining, granite, gneiss, schist, fossiliferous Silurian grits and shale with igneous (diallage) rocks, and conglomerates. There is also, in a boss of primary rocks at the north-west corner of this townland, a small mineral vein containing lead ore, and a trace of copper and mundic.

"Good Silurian fossils, supposed to be of Upper Llandovery age, have been found at Currareavagh and New Village in Glan, on the west of the lake; also at Kilbride, on Loch Mask; Benlevi, more especially about Coolin Loch, and from that to Ashford Demesne; also in Lisloughery, and Gortachurra townlands, and the adjoining islets. West of Ashford rare trilobites occur; and in the carboniferous limestone in that demesne I was fortunate enough to find a Chiton, this being the second locality where chitons are recorded as found in the carboniferous limestone, the other being near Rathkeale, Co. Limerick. Black limestone, that will take a fine polish, and form good marble, occurs at Menlough and Anglingham, which quarries are at present worked; also at Rushveala and Cregg, near Oughterard. The serpentine, or green calcareous rocks, commonly called `Connemara marble,' are found in various places between Lissoughter and Clifden; and at present a company is about to open works on these at Lissoughter and Ballinahinch, whence it is intended to carry the blocks to the sea, and ship them at Cashel, near Roundstone.

"In the primary rocks, and in some of the carboniferous limestone adjoining the lake on the north, nort-west and east, mineral indications are frequent; but up to the present no deep workings have been carried out, therefore it is impossible to speak positively on the mineral resources of the district. In the carboniferous limestone, on east of the lake, lead and sulphur ores have been found in the neighbourhood of Ballycurran; and on the west of the lake, at Gortmore, Drumeillstown, Moyvoon, Portacarron, Lemonfield, Ardvarne, and Eighterard, and in most of these places small trials have been made on the veins. In all the primary rock the indications of lead, copper, and sulphur are more or less plentiful, and small trials have been made at Doorus, and other places on the north of the lake. At Leackavrea, and in Glann, Mr. Hodgson carried on mining operations for some time, and shipped some copper and sulphur ore from the port of Galway, having for the time a steamer plying on the lake to carry the ore to that port. During his operation the hills were burrowed in various directions, and more money spent than, if put in a deep working, would have proved whether the country contains good mines or not. The deepest working in the district is that at Glangowla, in Mr. O'Flahertie's mine, where large bunches of lead were found some years ago." His mines at Cregg and Cranrower are at present let to a Glasgow Company.