44 



HELLER 



made by sea urchins, are now several hundred feet above the 

 present sea level. Much erosion has taken place, especially 

 about Wenman and Culpepper which formerly were consider- 

 ably larger than they are now. Wenman appears to have once 

 been the central crater of a larger island. Its steep semicircular 

 northern face is not the result of erosion but at one time it formed 

 the southern wall of the crater whose northern rim has been 

 eroded away. It is only a short time, geologically speaking, 

 since ihe northern and southern portions of Albemarle were 

 united by the low Perry Isthmus which has the appearance of 

 being built up from a recent lava flow from the southern crater. 

 Had the central crater of Narboro continued active for some time 

 longer it would have poured out lava enough to fill the narrow 

 strait separating it from Albemarle, thus uniting those two 

 islands. 



Ag-e of the Archipelago. — In the absence of any available 

 geologic evidence as to the age of the archipelago the degree 

 of differentiation attained by the fauna may be taken as indica- 

 tive of considerable age. This kind of evidence is most notice- 

 able among the reptiles. The greatest differentiation is shown 

 by the genera A^nblyrhyfichus, Conolophus and Testudo while 

 some of the others, perhaps later arrivals, as Orophis, Tropi- 

 durus and some of the Phyllodactyli shoyv little or no differentia- 

 tion from continental species. From the prominent West Indian 

 element in the fauna and flora, which may have reached the 

 islands during that part of the Tertiary when the Americas were 

 separated, it would appear that the archipelago is at least of 

 Tertiary age and the presence of Testudo would also support 

 this view. 



Previous Expeditions. — Previous to Darwin's visit to the 

 Galapagos in 1835 ^ f^w reptiles, mostly Testudo, had been 

 collected by navigators and presented to various museums. 

 Darwin's collection formed the basis for the first systematic ac- 

 count ^ of the herpetology of the archipelago and consisted of 

 specimens from Chatham, Charles and James. 



Later, in 1852, Dr. Kinberg of the Swedish frigate Eugenie 

 visited the archipelago and collected reptiles on Albemarle, 



'Bell, Zool. Beagle, Reptiles, 1843. 



