MINUTE STRUCTURE OF CORAL-LIMESTONE FROM BARBADOS. 243 



tho two oceans were united, a portion of the Gulf -stream may have 

 been diverted into the Piicitic, giving* rise to a current, some part of 

 which would almost certainly have reached the Galapagos, and this 

 may have helped to bring about that singular assemblage of West- 

 Indian and Mexican plants now found there." To the evidence of 

 the plants may be added the singular fact that since Mr. Wallace 

 wrote his " Island Life " gigantic land-tortoises similar to those 

 •of the Galapagos have been found in a sub-fossil state in one of the 

 Antilles. 



The consideration of the different physical conditions which must 

 fit the same time have prevailed in the North Atlantic is a still 

 more interesting problem for British geologists. It is possible that 

 a small circulatory system, similar to that which occurs in the 

 North Pacitic, may then have existed iu the southern part of the 

 North Atlantic between Africa and Plorida, but it would be on a 

 ■comparatively small scale, and any small offshoot that it maj' have 

 sent toward the coasts of Europe could not have exercised much 

 ameliorating influence on the climate of those coasts. 



The Arctic currents must have been all-powerful in the Atlantic 

 north of lat. 40°, and such conditions are sufficient to account for 

 the extreme rigour of the Glacial period in the British Islands and 

 Northern Europe. We are not here suggesting a geographical 

 explanation of the Glacial period, because the evidences of that 

 period occur over the whole of the northern hemisphere, but it has 

 often been pointed out that, in the absence of the Gulf- stream, 

 Britain would be left with the cb'mate of Newfoundland and 

 Labrador. This very absence of a Gulf-stream, which has only 

 hitherto been suggested as a possibility, follows as a necessary con- 

 sequence from our restoration of Caribbean geography in early 

 Pleistocene time, and that is based on definite geological facts. 



The nature of the deposits which were formed during the great 

 period of submergence that preceded the upheaval confirms the 

 theory of previous open communication with the Pacific, and of 

 these deposits we hope to treat in a future paper. 



APPENDIX I. — On the Minute Structure of some Coeal-Lime- 

 STONES from Barbados. By William Hill, Esq., E.G.S. 



[Plate IX.*] 



The following is a brief description of the minute structure of the 

 coral-rocks of Barbados which have been sent me for examination ; 

 fiome were obtained by Mr. Jukes-Browne, and some more recently 

 procured by Mr. Edw. Easton, C.E., from the shafts and tunnels 

 made by the Barbados Water-Supply Company. 



They are, as a whole, hard white crystalline limestones, generally 

 full of cavities, caused apparently by the solution of some of the 

 calcareous structures of the many organisms of which the rocks 

 were formed. 



It is hardly possible to say, from a microscopic examination only, 



* This plate is presented by Mr. Hill. 



