ON A PIECE OF CHALK 61 



drive a wagon all the way from Valentia, on the west coast 

 of Ireland, to Trinity Bay, in Newfoundland. And, except 

 upon one sharp incline about 200 miles from Valentia, I am 

 not quite sure that it would even be necessary to put the skid 

 on, so gentle are the ascents and descents upon that long route. 5 

 From Valentia the road would lie downhill 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 10 

 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 water. Beyond this, 

 the ascent on the American side commences, and gradually 

 leads, for about 300 miles, to the Newfoundland shore. 15 



Almost the whole of the bottom of this central plain (which 

 extends for many hundred miles in a north and south direc- 

 tion) is covered by a fine mud, which, when brought to the 

 surface, dries into a grayish white friable substance. You 

 can write with this on a blackboard, if you are so inclined ; 20 

 and, to the eye, it is quite like very soft, grayish chalk. 

 Examined chemically, it proves to be composed almost wholly 

 of carbonate of lime ; and if you make a section of it, in the 

 same way as that of the piece of chalk was made, and view it 

 with the microscope, it presents innumerable Globigerince 25 

 embedded in a granular matrix. 



Thus this deep-sea mud is substantially chalk. I say sub- 

 stantially, because there are ^ good many minor differences ; 

 but as these have no bearing on the question immediately 

 before us, which is the nature of the Globigerina of the 30 

 chalk, it is unnecessary to speak of them. 



Globigerincz of every size, from the smallest to the largest, 

 are associated together in the Atlantic mud, and the cham- 

 bers of many are filled by a soft animal matter. This soft 



