4 Proceedings of the Royal Physical Society. 



and migrations of marine floras and faunas. In the slow 

 continuous creep of icy polar water towards the equator, 

 and the drift of warmer surface-water towards the poles, the 

 system of oceanic circulation presents itself under a wholly 

 unexpected aspect to the geologist. Moreover, he is taught 

 that, where the configuration of the bottom permits, an 

 arctic and a temperate fauna may co-exist at the same depth, 

 and within a mile or two of each other, kept apart by a 

 narrow interposed ridge that separates the cold from the 

 warmer water.^ The mere announcement of such facts as 

 these is suggestive of fruitful applications in geology. But 

 we must await the patient elaboration and final publication 

 of their results by the naturalists, who liave so skilfully 

 planned and so brilliantly accomplished their observations, 

 before we are in a position to comprehend the full geological 

 significance of the discoveries. 



o. A third fact of fundamental consequence recently 

 revealed to us is the prodigious abundance of life in the 

 surface-waters of tropical ocean -currents. I shall have 

 more to say on this subject in the sequel. I may in the 

 meantime remark, that the fact is important because tlie 

 profusion of pelagic life implies a copious supply of food 

 to higher forms, and consequently an abnormally abun- 

 dant fauna in the track of the currents. Food is thus 

 shown to be a far more efficient cause in determining the 

 development of life than some of the more recondite 

 influences which are often invoked.- From the analogy of 

 the existing sea-bottom we may infer that ancient wide- 

 spread limestones, composed of crinoids, corals, foraminifera, 

 mollusks, and other organisms, were not formed in closed seas, 

 but rather in areas of no great depth, across which currents 

 could bring an abundant supply of food from the main 

 ocean. Viewed from this side, such a formation as the 

 Carboniferous Limestone acquires a fresh interest. The 

 thick calcareous mass that stretches from the west of Ireland 

 into Westphalia, instead of marking the site of a supposed 



1 See Mr Murray's Paper on the Wyville Thomson ridge (Proc. Roy. Soc, 

 Edink, 1882, vol. xi., p. 638). 



- See A. Agassiz (Trans. American Academy, 1883, vol. xi.). 



