^%r''] PROCEEDINGS OF THE NATIONAL MUSEUM. 355 



and Culpepper, and tlie two other j>roups of islands we have recog- 

 nized." 



******* 



"While slowly steaming through tlie archipelago from island to island 

 we had an excellent opportunity of studying the natural features of 

 these islands, and also as we passed their shores or were dredging 

 within a moderate distance. As ftir as a cursory examination like ours 

 could prove anything regarding the nature of the geological structure 

 of the islands, our observations fully agree with those of Darwin and 

 of Wolf, that this group presents one of the best examples of true vol- 

 canic islands. 



"The majority of the islands are evidently formed around a central 

 crater or center of elevation. They have increased in size and in height 

 from successive lava Hows. There is nothing to show that the sepa- 

 rate islands are entirely the result of the disintegration of a larger 

 volcanic chain, though of course a ceitain amount of denudation and 

 sul)marine erosion has undoubtedly taken place, as is readily seen on 

 the sloj)es of the islands and on examination of the soundings between 

 them. Neither do we find any indications either of elevation or of 

 subsidence of any part of the area of the Galapagos district which 

 would affect their topography; and, as Wolf maintains, we can still less 

 explain their formation by a separation in former i)eriods from the 

 South American continent. On the contrary, every part of their struc- 

 ture seems to prove that the islands have been slowly formed by sub- 

 marine eruptions at first, and subsequently by similar accretions at 

 the level of the sea, until finally some of the islands have reached an 

 elevation of over 3,000 feet. During the process of growth some of the 

 islands have become joined together, as for instance Albemarle, which 

 is probably composed of three islands originally independent, and also 

 the eastern and western i)arts of Chatham, which were surely once two 

 separate islands, and are now connected only by a low isthmus. 



"The volcanic activity of some of the islands has continued to com- 

 l)aratively very recent tinu\s. 1 am informed by Mr. Cobos that smoke 

 has been seen to issue from Narborough as late as 1S30, and it is well 

 known that Capt. Collet was driven from Tagus Cove by the heat due 

 to an eruption on the neighboring Narborough. It is quite probable 

 that the age of the CJalapagos does not reach beyond the earliest Ter- 

 tiary period, and many parts have undoubtedly not been formed before 

 the present epoch, so that the time is geologically short during which 

 so many plants have developed from their South American, their Cen- 

 tral American, their Mexican, or their West Indian ancestors. " * 



CLIMATOLOGY AND FLORAL ASPECT. 



As would be sui)posed, the climatology of these islands is peculiar. 

 Though situated directly on the equator, it is not excessively hot, being 



*A. Agassiz. 



