PHOTOGRAPHY OF OCEAN FLOOR — LAUGHTON 323 



origin, and muck work 1ms been done to elucidate its structure but 

 without any conclusive results. Photography has shown that its 

 rocky peaks are areas of extremely low sedimentation and have been 

 subject to recent and violent upheaval. Plate 3, figure 1, shows 

 steep slopes and freshly cleaved rocks resembling the screes found on 

 land. Other photographs have shown basins of sediment covered with 

 patches of shinglelike material that may in fact be colonies of a deep- 

 sea shellfish. On the whole the rocky peaks appear poor in sessile 

 fauna, a fact consistent with the idea of a geologically recent 

 disturbance. 



By far the most interesting and varied collection of sea-bottom 

 photographs has been taken on the volcanic seamounts that rise out 

 of the deep basins. In general the greater the depth, the less dense 

 is the f aunal population. The attraction of a seamount to the abyssal 

 fauna is doubtless partly related to its geological formation. There 

 are a great many exposed rocks and boulders in varying states of 

 fracture; there are sands and oozes in great variety. These offer 

 to the famia a variety of footholds and, to fishes, shelter in which to 

 hide from their foes. Possibly nutrients are concentrated in the 

 water in these regions by local up welling due to obstruction of the 

 waterflow and by the solution of minerals from the rocks themselves. 

 Examples are shown of the continuous type of submarine lava flow, 

 of the bedrock, of broken boulders and shingle, and of the current- 

 swept sand with ripplemarks. Often it appears that the fauna of 

 one seamount differs from that of another and that where in one place 

 for instance one finds predominantly crinoids, in another there may 

 be sponges. However, this differentiation may be only the result of 

 inadequate sampling techniques, and until more pictures are taken it 

 cannot be confirmed. Photographs taken on seamounts are illustrated 

 in plate 3, figure 2, plates 4, 5, and 6, plate 7, figure 2, plate 8, and 

 plate 9, figure 1. 



Photogi-aphs w^ere taken of one bank of especial interest off Cape 

 Finisterre. Galicia Bank, which is divided from the Continental 

 Shelf by a depth of 1,500 fathoms, has a structure that may be related 

 more nearly to that of the continent than to that of the ocean floor. 

 Rocks dredged from it are of two distinct types; limestones and a col- 

 lection of dark metamorphic rocks. The jihotographs strongly sug- 

 gest that the limestone is locally derived, wdiereas the metamorphic 

 rocks are erratic and have possibly been carried by icebergs from the 

 north. (PI. 9, fig. 2.) 



SPECIAL PROBLEMS 



The geological interpretation of rocks seen in bottom photograplis 

 is extremely difficult unless hand specimens can be examined. How- 



