168 On the Composition of Oceanic 



and the deep channel contract until they reach a minimum of 

 sectional area, where this deep spot is. Here the whole width 

 across from Skate Island to the south shore is only 1-6 mile, 

 and of this one-half, or 0-8 mile, is occupied by a shallow 

 tongue, with about 20 fathoms, projecting from the south 

 shore. The deep channel, with over 50 fathoms, is here con- 

 tracted to little over 0-3 mile. It will be seen from these data 

 that dredging in the deepest water is difficult, because it implies 

 drifting ; and as the deep channel, besides being narrow, makes 

 here a sort of elbow or sinuosity, as if there had been foldings 

 in a vertical plane, it would seem to be impossible, as I generally 

 found it to be in practice, to drift for any distance in any 

 direction without rapidly getting into shallower water. 



The chart is taken from Admiralty Charts Nos. 2133 and 

 2321, on the scale of 2 inches to the sea mile. The areas from 

 the shore on both sides of the loch to the contour line of 

 30 fathoms is left unshaded; that lying between the contours 

 of 30 and 80 fathoms is lightly shaded and areas enclosed by 

 the contour of 80 fathoms are darkly shaded. The great 

 constriction at Skate Island, with the deepest spot lying 

 immediately on one side, is well shown both in the map and 



Loch Fyne. Section II. Cantyre to Cowal through 2o-fathom 

 bank and Skate Island. 



in Sections II and III. In Section II the area of the whole 

 section is 52,190 square fathoms; that of water lying at a 

 greater depth than 30 fathoms is 17, goo 1 square fathoms. 



1 In marine charts the unit of distance is always the nautical mile, 

 which is equal to one minute of arc of a great circle of the globe, and it is 

 subdivided into 10 cables of 100 fathoms each ; so that the nautical mile is 

 1000 fathoms. Hence, in applying the decimal system to geographical 

 measurements, the fathom is the natural unit so long as we retain the 

 subdivision of the circumference of the circle into degrees and minutes as 

 at present. The metre and kilometre are very inconvenient and clumsy in 

 this respect 



