642 DR HUGH ROBERT MILL ON THE 



the coast of Ireland, gives access to the Irish Sea. A line drawn from the peninsula 

 of Cantyre to the nearest point of the Einns is 23 miles long, nearly parallel to 

 the Irish coast from Fair Head to Belfast Lough, and marks the southerly boundary 

 of the region under consideration. It thus appears that currents sweeping through the 

 North Channel from the Atlantic to the Irish Sea, or vice versa, set across the entrance 

 of the Clyde Sea Area. From the southern boundary line the channel extends north- 

 ward, divided by the large and mountainous island of Arran into the narrow Kilbrennan 

 Sound on the west, and the w T ider expanse of water usually termed the Firth of Clyde 

 on the east. Bute, Inchmarnoch, and the Cumbraes, smaller islands lying farther north, 

 split up the channel into narrow sounds, which are continued inland by a remarkable 

 series of deep inlets which run northward into the mountainous peninsula of Cowal. The 

 north-western corner of the channel is prolonged into the inlet called Loch Fyne, which 

 curves toward the north-east, and the north-eastern corner extends into the straighter and 

 narrower Loch Long. The latter inlet running nearly north, is joined from the east at 

 right angles by the shallow estuary of the Clyde, which is the only large river entering 

 the area. The name " Firth of Clyde," as usually applied, must be understood as 

 referring to a totally different physical feature from the "Firths" of Forth or Tay. The 

 Sea Area has no more intimate physical relation with the river after which it is named 

 than the North Sea has with the Thames or the Rhine. 



The Clyde Sea Area falls into certain natural regions distinctively marked out by 

 their configuration, and only corresponding in part with the topographical divisions that 

 are familiarly employed. The sketch-map (Plate I.) shows the relation of the two systems 

 of partition ; and in what follows, the physical rather than the topographical names will 

 be usually employed. In this paper I follow the orthography of the Admiralty Charts 

 for place-names ; but the maps prepared by Mr Bartholomew, being reduced from the 

 Ordnance Survey, give different spellings in some cases. 



The entire Sea Area includes about 1160 square miles, or 881 square sea miles, of water 

 surface, toward which 3350 square miles of land surface slope. The total volume of water 

 in the Area at low tide, estimated from data which will be described later, is about 25 '5 

 cubic sea miles, and the average depth is 29 fathoms. At high water, about 1*15 cubic 

 sea miles of water are added, and the average depth is increased to 30^ fathoms. 



The contoured map (Plate II.) shows that we can distinguish the following regions 

 under the water surface, some of them being more distinct than others ; and that they 

 fall into the two classes — submarine plateaux and deep channels or basins. The plateaux 

 serve to separate the basins, and in most cases they are merely narrow bars, which it is 

 unnecessary to consider separately. The basins consist either of one narrow straight 

 trough, or of a succession of more or less distinct depressions in one line, or they may be 

 branched and curved ; but all are alike in being much elongated in one direction : — The 

 most important physical divisions are : — The Great Plateau, the Arran Basin, Loch Fyne 

 Basin, Kyles of Bute and Loch Ridun, Bute Plateau, Loch Strivan Basin, Dunoon Basin, 

 Holy Loch, Loch Long Basin, Loch Goil Basin, Estuary, Gareloch Basin. 



