7:M DB JOHN MURRAY AND MR ROBERT IRVINE ON THE 



A most extensive series of dredgings was conducted during several years in nearly 

 all parts of the Clyde Sea-Area, and so constant were the conditions under which the 

 manganese deposits occurred that Captain Turbyne, of the yacht " Medusa," could usually 

 point out with certainty the situations in which they might be procured by the dredge. 

 There is one apparent exception, viz., the very deepest spot in the whole area (106 

 fathoms), in Lower Loch Fyne. The nodules from this place were described several years 

 ago by Mr J. Y. Buchanan. * This deep hole is very limited in extent, and the nodules 

 found in it occur only in one place, and that at the very deepest point. The hole is 

 situated off Skate Island, towards which, from the Cantyre shore, there runs a submerged 

 tongue or ridge, so that the water passing through this narrow gully to supply the whole 

 of the upper parts of Loch Fyne is much confined, and motion of the water takes place 

 at a greater depth here than at other parts of the area. With reference to currents, then, 

 this deep hole resembles the hollows filled with mud on the ridges and barriers, t 



In addition to the deposits of manganese dioxide on stones, and in the form of 

 nodules, many of the living and dead shells found in the deeper parts of the district are 

 coated with this substance — for instance, those of Astarte sulcata, Nucula sulcata, Pecten 

 septemradiatus, Cyprina islandica, Corbula gibba, Venus fasicula, Venus casina, Scro- 

 bicularia alba, Buccinum undatum, Fusus antiquus. Many of the dead fragments of 

 Lithothamnion calcareum from the shallow dredgings are black coloured, and thoroughly 

 impregnated with deposits of manganese dioxide. 



A survey of the foregoing facts seems to show conclusively that the bicarbonate of 

 manganese, which we have found in solution in the sea-water associated with the Blue 

 Muds of the Clyde sea-basins, has been derived either from the deoxidation of the 

 dioxide carried into the sea by streams along with other detrital matters, through the 

 decomposition of organic matter in the presence of the sulphates of the sea-water, or 

 directly from decomposition in the mud of manganese-bearing silicates present among the 



* See Buchanan, Trams. Roy. Soc. Edin., vol. xxxvi. p. 459, 1891. 



t Captain Turbyne, of Mr Murray's yacht "Medusa," writes as follows as to the manganese dredging in the Clyde 

 Sea-Area : — " Regarding the nodules being in pot-holes, I consider that I have absolute proof of that on the outer side 

 of the barrier of Loch Goil. In the first place, we were dredging from the outside toward the barrier or up the loch, 

 on the slope, as I thought, between the mud and harder ground. In this case we ought to have been shallowing our 

 soundings, but after towing for a short time the dredge suddenly began to dip, which was seen from the angle of tin- 

 wire, and more had to be run out ; then we suddenly came fast, and had to heave up, and this was the haul in which 

 the nodules were got. They differed from those at Skelmorlie Bank in being much larger, and to the unaided eye 

 they seemed perfectly smooth and quite round. In the second place, after finding the nodules I tried to get more botli 

 OH this and on several other occasions ; but though we tried to strike the spot as nearly as possible, it was only after 

 dredging up and down the loch and in close sections across it, that we again hit on the spot. For these reasons I have 

 come t<p the conclusion that the nodules are found in a hole of small extent. This is the only instance in my experience 

 in which I am certain that the nodules were taken from a small hole. In my opinion the slopes of Skelmorlie Bank 

 and Minard Narrows are full of small holes containing mud and manganese nodules where the tide meets with an 

 obstruction. The 106 fathom-hole has always been a mystery to me. I often thought that if the nodules were formed 

 in I hat, deep hole, why don't we get them off Brodick in 95-97 fathoms, which part is practically a continuation of the 

 trough in which the 106 fathom-hole is situated 1 Surely this submarine tongue you mention and the small size of 

 the L06 fathom-hole has got something to do with it. I can say nothing about under-currents at the deep hole, but 

 there i- a Btrong surface-current at spring-tides, as we rapidly got out of position, and it is well known to fishermen 

 and others that, with the wind against the tide, a nasty sea is met with off Skate Island." 



