112 THE MICROSCOPE. 



that the chalk-forming process is even now going 

 on at the bottom of the North Atlantic Ocean 

 over an immense area, and this is brought about for 

 the most part by the same agencies as built up the 

 hills and deposits of the Cretaceous period. This 

 deep-sea mud is substantially chalk, and covers an 

 area of about 1,700 miles from east to west. " It is a 

 prodigious plain one of the widest and most even 

 plains in the world. If the sea were drained off, you 

 might drive a wagon all the way from Valentia, on the 

 west coast of Ireland, to Trinity Bay, in Newfound- 

 land. And except upon one sharp incline about 200 

 miles from Valentia, I am not quite sure that it would 

 be necessary to put the skid on, so gentle are the 

 ascents and descents upon that long route. From 

 Valentia the road would lie down-hill for about 200 

 miles to the point at which the bottom is now covered 

 by 1,700 fathoms of sea-water. Then would come 

 the central plain, more than a thousand miles wide, 

 the inequalities of the surface of which would be 

 hardly perceptible, though the depth of water upon it 

 now varies from 10,000 to 15,000 feet; and there are 

 places in which Mont Blanc might be sunk without 

 showing its peak above the water. Beyond this, the 

 ascent on the American side commences, and gradually 

 leads, for about 300 miles, to the Newfoundland shore. 

 " Almost the whole of the bottom of this central plain 

 (which extends for many hundred miles in a north and 

 south direction) is covered by a fine mud, which, when 

 brought to the surface, dries into a greyish-white friable 

 substance. You can write with this on a blackboard 

 if you are so inclined, and to the eye it is quite like 

 very soft, greyish chalk. Examined chemically, it 

 proves to be composed almost wholly of carbonate of 

 lime ; and if you make a section of it, and view it with 

 the microscope, it presents innumerable Globigerinae 



