AND RIVEE VALLEYS BOEDEKING THE EEITISH ISLES. 309 



gently descends to a depth of about 1,600 fathoms or 9,600 

 feet; the form and height of the escarpment are similar to 

 those of Section VII, but somewhat steeper. 



No. 3. This section is remarkable for two points ; first, the 

 width of the British platform, and the depth of its western 

 margin below the ocean surface. It is drawn from the coast 

 of Clare (where the cliffs of Moliir, formed of Carboniferous 

 sandstone, rise 400 feet above the sea) along a series of 

 soundings stretching due west for a distance of 280 miles. 

 The platform is here about 200 miles across, and its western 

 margin is indicated by the 200 fathom contour very nearly ; 

 that is twice the depth of the margin opposite Donegal and 

 the Hebrides. The escarpment here, just west of the 

 " Porcupine Bank," is very bold and lofty ; descending 

 abruptly from the 200 to the 1,500 contours, being a total 

 descent of about 7,800 feet. Directly north of the Porcupine 

 Bank, the escarpment is quite precipitous, as the two 

 terminal contours (the upper and lower) are in close 

 proximity. With this tremendous descent of over 7,000 

 feet, the escarpment stretches southward, till opposite the 

 south of Ireland it sweeps round eastward, producing a wide 

 bay about 200 miles across, and sloping upwards to the 

 marginal line of 200 fathoms, at which point the old channel 

 of the river Shannon seems to have descended to the ocean 

 when this was emergent land. Opposite this bay the floor 

 of the ocean descends to a depth of 2,500 fathoms (or 15,000 

 feet) within a distance of 200 miles. 



No. 4. This section is drawn from the coast of Kerry in 

 a south-westerly direction, and is continued eastward over 

 Carantual, the highest mountain in Ireland, reaching a height 

 of 3,400 feet above the sea. The platform is here only 60 

 miles across, and the descent from its margin is less precipi- 

 tous than in the case of Sections 2 and 3. The depth of 

 the margin is about 200 fathoms, and after the initial steep 

 descent to about 1,500 fathoms, the ocean bed gently declines 

 till, at a distance of 170 miles from the margin, it reaches a 

 depth of 2,300 fathoms or 13,800 feet. This is the last of the 

 sections I have drawn; but if another were taken in a south- 

 westerly direction from Ushant, off the coast of France, it 

 would show a platform of 80 miles in breadth, breaking ojEF 

 at the 200-fathom line in a sheer precipice of 5,000 feet just 

 south of La Eochelle Bank, which is situated at the edge of 

 the platform itself. 



We have now reached the southern limit of the region 



