462 MR J. Y. BUCHANAN, F.R.S., ON THE 



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 contracted to little over 

 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. Where the depth is less than 30 fathoms it has been left 

 uncoloured, depths over 30 fathoms have been coloured blue, aud those over 80 fathoms 

 dark blue, showing the trend of the deepest parts. The great constriction at Skate 

 Island, with the deepest spot lying immediately on one side, is well shown both in 



S 4-7? W .. ^-^ /"" N 4-7 ° E 



Loch Fyne. Section II. — Cantyre to Cowal through 20-fathom bank and Skate Island. 



the map and 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 17,940 * square 

 fathoms. In Section III. these quantities are 61,500 and 21,500 square fathoms. For 

 comparison with these we have Section I. at the mouth of Loch Fyne and Section VI. at 

 the widest part, towards Loch Gilp. In the former of these the total area is 154,820 square 

 fathoms, and the area of water over 30 fathoms is 61,920 square fathoms ; in the latter 

 these figures are 129,200 and 67,500. Sections IV. and V. show transition stages from the 



=^ Z 



Section IIa. — The same as Section II. on natural scale. 



narrowest to the widest portions of the landward portions of the loch. Section IIa. is 

 constructed on a uniform scale of lengths and depths, and gives the natural proportions 

 at the narrowest points. 



* 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 kilo- 

 metre are very inconvenient and clumsy in this respect. 



