GEOL OGICA L CONCL USIONS. 



311 



The Rev. John WilHams states that there are seven or eight of 

 large extent on the island. Into one he entered by a descent 

 of twenty feet, and wandered a mile in one only of its branches 

 without finding an end " to its interminable windings." He says, 

 " Innumerable openings presented themselves on all sides as 

 we passed along, many of which appeared to be equal in height, 

 beauty, and extent to the one we were following. The roof, a 

 stratum of coral rock fifteen feet thick, was supported by massy 

 and superb stalactitic columns, besides being thickly hung with 

 stalactites from an inch to many feet in length ; some of these 

 pendents were just ready to unite themselves to the floor, or to 

 a stalagmitic column rising from it. Many .chambers were 

 passed through whose fretwork ceilings and columns of stalac- 

 tites sparkled brilliantly, amid the darkness, with the reflected 

 light of our torches. The effect was produced not so much by 

 single objects, or groups of them, as by the amplitude, the 

 depth, and the complications of this subterranean world." 



Other similar caves exist on the neighbouring island of 

 Mauke. 



The Bermudas are also noted for their caverns. The coral- 

 made land here stands in some places 260 feet above the sea. 

 Lieutenant Nelson speaks of the caverns as large and beautiful 

 — one of them "a perfect bijou." 



These are examples of the comparatively rapid formation 

 of caverns. The waters which run or perx;olate through them 

 must be charged with carbonic acid to accomplish such work, 

 and yet they have no source for this ingredient except. the atmo- 

 sphere, animal respiration, and vegetable and animal decom- 

 position in the soil. The flutings and stalactitic incrustations 

 of a precipice facing the sea must depend on the former alone, 

 with the aid perhaps of the spray from the sea brought over 

 the reef by storms. 



XIII. OCEANIC TEMPERATURE. 



Facts seem to indicate — though perhaps not sufficient to 

 demonstrate — that the Gulf Stream has had, from the Jurassic 



