1891.] The Origin of the Galapagos Islands. 219 
1875, states that Narborough still has an active central crater of 
enormous size. Most ofthe islands consist of basaltic rocks and 
masses of scoriz and lava, but besides we find, according to Wolf, 
remains of an older volcanic formation on Charles Island and the 
small islands Gardner, Caldwell, and Enderby, which surround it. 
Dr. Th. Wolf, the state geologist of Ecuador, visited the islands 
twice, according to a letter received from him. He spent in all 
six months on the group,—more time than any other visitor, Dr. 
Habel excepted. He published a small pamphlet about the 
islands in 1879 (Ein Besuch der Galapagos-Inseln. Heidelberg, 
1879, 44 pp., 3 maps). The following account about the climate 
is taken principally from him and from “The South American 
Pilot.” . ; 
The climate, considering that these islands are directly on the 
equator, is far from being excessively hot, a circumstance which 
is chiefly owing to the singularly low temperature of.the surround- 
ing sea, which is 23° C. On Charles Island at an elevation of 
140 m. the thermometer was 19-21° (about 68° F.), and at about 
300m. 18-19°. Darwin observed a heat of 34° C. (93° F.) in his 
tent when the thermometer stood at 29° C. in the wind and sun, 
but which, when plunged in the soil, rose at once to 58° C., and 
would probably have risen higher had the tube been longer. 
The rainy season is between February and June, but is very 
irregular, generally very short, and often it stops entirely for one 
or two years. ‘In the higher portions of the islands, about 270 m., 
there is often rain all the year, but very little. In August and Oc- 
tober Wolf observed such squalls, so-called “garruas,” very often. 
They repeated each other often five or six times in a day, but never 
lasted more than half an hour. They are confined to the high 
plateau. The whole broad lower zone up to 170 m. is nearly 
without any rain; therefore the upper region remains always green, 
the lower one arid and barren. On the southeastern parts of the 
islands, on the side of the southern trade-winds, the damp region 
‘extends nearly 70m. more down than on'the northern side. It is 
evident that the conditions of the vegetation are dependent upon 
this different distribution of humidity. Near the border of the sea 
-we find different maritime plants ; in-some of the bays mangrové& 
