THE GEOLOGY OF BERMUDA. 29 



tion, I believe, is satisfactorily answered iu the exiilanation I have given. 

 Sir AVyville Thomson's explanation I transcribe entire, lest I should do 

 injustice in criticizing a passage which I do not quite understand. "In 

 the caves in the limestone, owing to a thread of water having found its 

 way iu a particular direction tlirough the porous stone of the roof, a 

 drop falls age after age on one spot on the cave-floor accurately directed 

 by the stalactite which it is all the time creating. The water contains 

 a certain proportion of carbonate of lime, which is deposited as stalag- 

 mite as the water evaporates, and thus a ring-like crust is produced at 

 a little distance from the spot where the drop falls. When a ring is once 

 formed, it limits the spread of the droj), and determines the iDOsition of 

 the wall bounding the little pool made by the drop. The floor of the 

 cave gradually rises by the accumulation of sand and travertine, and 

 with it rise the walls and floor of the cup by the deposit of successive 

 layers of stalagmite; and the stalagmite produced by the drop perco- 

 lating into the limestone of the floor hardens it still further, but in this 

 peculiar symmetrical way."* On this explanation I will only remark 

 that stalagmites deeply and broadly concave on the top, and cave-floors 

 rising by accumulation of sand and travertine (the material having the 

 structure of drift sand-rock) so as to keep nearly on a level with the grow- 

 ing bosses of stalagmite, are phenomena never observed, to my knowl- 

 edge, in Bermuda or elsewhere, 



NON-CALCAREOUS ROCKS AND MINERALS. 



While the only indigenous rocks in Bermuda are the various varie- 

 ties of limestone, the "red earth," and the peat or muck of the bogs, 

 grains and nodules of various minerals, mostly volcanic in origin, occur 

 mingled with the coral sands, and blocks of various rocks are liable to 

 be occasionally brought in the roots of drifted trees. These accidental 

 arrivals are common to all oceanic islands. 



John Murray, F. R. S. E., in a letter to General Sir J. H. Lefroy (a 

 copy of which has been furnished me by the kindness of J. Matthew 

 Jones, F. L. S.), names the following minerals as occurring in samples 

 of Bermuda sands examined by himself: menaccanite, magnetite, au- 

 gite, olivine, hornblende, sanidin and other feldspars, mica, and per- 

 haps quartz. Mr. Murray notes the fact that the "red earth," on treat- 

 ment with acids, leaves a residue much resembling the " titaniferous 

 sands " found at various localities along the shore. He suggests that 

 the volcanic minerals of the " titaniferous sands" may have been iu 



* Op. eit, Vol. I,, pp. 308,309. 



