On a Piece of Chalk 83 



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 gradu- 

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



Almost the whole of the bottom of this central plain 5 

 (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 grayish-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 10 

 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 embedded in a granu- 15 

 lar matrix. 



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

 substantially, because there are a good many minor dif- 

 ferences; but as these have no bearing on the question 

 immediately before us, which is the nature of the Globi- 20 

 gerince of the chalk, it is unnecessary to speak of them. 



Globigervue of every size, from the smallest to the 

 largest, are associated together in the Atlantic mud, and 

 the chambers of many are filled by a soft animal matter. 

 This soft substance is, in fact, the remains of the creature 25 

 to which the Globigerina shell, .or rather skeleton, owes 

 its existence and which is an animal of the simplest 

 imaginable description. It is, in fact, a mere particle 

 of living jelly, without defined parts of any kind with- 

 out a mouth, nerves, muscles, or distinct organs, and only 30 

 manifesting its vitality to ordinary observation by thrust- 

 ing out and retracting from all parts of its surface, long 

 filamentous processes, which serve for arms and legs. 

 Yet this amorphous particle, devoid of everything which, 



