12 THE FLOOR OF THE OCEAN 



made by the British ship "Challenger." Sir John Murray, 

 member of the expedition and editor of the report in many 

 royal-quarto volumes, classified the different kinds of sediment 

 and published a map of their distribution over the world. 

 Murray defined deep-sea deposits as those dredged from depths 

 greater than ioo fathoms or 600 feet, and forming two groups. 

 The one group he named "terrigenous," since these represent 

 detritus from lands which are respectively not far distant. The 

 other group, named "pelagic," represents slowly accumulated 

 deposits in deep water, far from any land. Table II gives the 

 subdivisions. 2 



Table II 

 Murray's classification of deep-sea deposits 

 Terrigenous Group: Pelagic Group: 



Blue Mud Globigerina Ooze 



Red Mud Pteropod Ooze 



Green Mud Diatom Ooze 



Volcanic Mud Red Clay 



Coral Mud • Radiolarian Ooze 



The deep-sea dredge gets its load while being dragged 

 along the bottom. It gives little information as to how the 

 character of the soft deposit varies with depth. To find the 

 nature of this variation we need an instrument based on the 

 principle of the cheese-sampler. If a long steel tube, lowered 

 and kept vertical all the way to the bottom, be forcefully 

 driven into the deposit, a sample, with the original layering 

 intact, can be trapped in the tube and brought to the surface for 

 study. Penetration of the loose sediment is accomplished in 

 either of two ways : by the automatic release of a heavy weight, 

 dropping on the head of the tube like a pile-driver; or by the 

 automatic firing of a "gun" charged with high explosive, the 

 hollow tube being the "bullet." Both methods give valuable 

 results, but here only the "gun" apparatus, invented by 

 Dr. C. S. Piggot, will be illustrated. 3 



