644 DR HUGH ROBERT MILL ON THE 



Loch Fyne. A few mountain burns from the granite heights of Arran — the area 

 of this island being about 160 square miles — and the shores of Cantyre (drainage 

 area 160 square miles), and Cowal (64 square miles), enter the narrow and deep 

 part of this basin ; but the wide shallow bay on its eastern shore receives the 

 Doon, the Ayr, and the Irvine — rivers which drain 690 square miles mainly of 

 Carboniferous strata, an area about equal to the water area of the basin. A narrow 

 isolated tract, exceeding 50 fathoms in depth, lies between Bute and the Cumbraes, 

 and a much larger X-shaped area of greater depth surrounds the north of Arran, and 

 occupies nearly one-third of the basin. The deepest water occurs in a straight trough 

 about half a mile wide, running nearly north-west for 20 miles through Bute Sound 

 and Inchmarnoch Water, terminating opposite Barmore Peninsula. Small isolated 

 depressions, lying in the same straight line, occur a few miles off each extremity of 

 the main trough, and of these, the southern, opposite Brodick Bay, will be frequently 

 referred to. The Arran Basin is a depression wide, shallow, and sloping very gently 

 in the south from the Great Plateau ; but toward the north it gradually becomes 

 narrower, deeper, and very much steeper in its descent from the shore. The maximum 

 depth of about 107 fathoms occurs two-thirds of a mile west of Skate Island, near 

 the northern extremity. The abruptness of this depression is strikingly shown in 

 section 19, C and D, Plate IX., which are on the same scale as the longitudinal sections, 

 and refer to direction nearly at right angles to the axis, crossing it at the point D. 

 Section 16, D, Plate IX., represents the same section on a natural scale, showing 

 the true slope, the steepest part of which appears to form an angle of 25°, or a 

 gradient of 1 in 3. This depression is the deepest in the Clyde Sea Area, and is 

 so small that shifting the position by 100 yards in any direction brings a vessel into 

 water shallower by 10 or 20 fathoms. By a fortunate coincidence, two white houses 

 on the Cowal shore are seen, at opposite extremities of a well-marked peninsula behind 

 Skate Island, from the deepest point, and this landmark enables the precise spot to be 

 picked up immediately in clear weather. The 685 square miles of water surface in the 

 Arran Basin receive the drainage of 1071 square miles of land, and the entire basin contains 

 18 cubic sea miles of water at low tide, and at high tide 0'7 more. The average 

 depth is 34 fathoms at low water, 35^ at high water, but along the axis of greatest 

 depth the mean is 68 fathoms. From its gradual narrowing and deepening toward 

 the north, the Arran Basin is particularly well situated for the free entrance of 

 sea water across the Barrier Plateau, and the abrupt descent in the narrow northern 

 region is an obstacle to land water getting access to the deeper parts. In the deepest 

 part the bottom is very fine mud, in which Mr J. Y. Buchanan has shown that 

 manganese nodules are comparatively abundant. 



Bute Plateau has a depth of about 20 fathoms, and stretches from the north end 

 of Great Cumbrae northward to Toward Point occupying Rothesay Bay. It separates 

 the Arran Basin from the basins of the north-east. The surrounding shores are low 

 and sandy, with no streams. Part of this plateau, with Rothesay Bay, is included 



