66 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



The 43 species of vascular plants known from Clarion Island have 

 been discussed in some detail by Johnston. The collection and notes 

 obtained by Elm.ore on the Allan Hancock Pacific voyage to that island 

 are listed below together with his collections from Socorro Island. As 

 with other spring collections from the island, their condition reflects 

 the dryness of that season. 



Socorro Island at about latitude 18°50' N and longitude 111° 

 00' W, stands as a rough quadrangular hulk (Plate 4, fig. 12). Fourteen 

 kilometers in length by about 11 kilometers in width, and with about 

 154 square kilometers of area, it is the largest of the Revilla Gigedo 

 group. Near the center is Mount Evermann, a little over 1138 meters 

 in elevation, a volcanic structure which Hanna (1926:56) and party 

 found mildly active in 1922. ''The whitish mud flows out in the side 

 of the gulch and makes a marker which Is visible for a long distance — . 

 The fissures are very active. We had no means of measuring the tem- 

 perature of the steam Issuing therefrom but the rush due to the high 

 pressure produced a great roar. Around the vents there was much 

 crystalized sulphur and the odor of hydrogen sulphide was very ap- 

 parent. The largest vents were about eight inches in diameter. In the 

 upper part of the gulch some of the fumaroles contained water but 

 this was found to be highly acid and entirely undrlnkable." 



The land form of the island is mountain broken up into ridges, 

 slopes, and radiating canyons. A small dry lake exists in an eastern 

 canyon. Recent and ancient lavas have contrasting soils and vegetations. 

 Permanent water is available at sea level at Gra5^son Cove on the south 

 side of the island, where a spring of fresh w^ater comes out of a crack 

 in the lava rocks. 



Sheep were introduced on the island in 1896 and were still running 

 freely about the island In considerable numbers in 1922. Grayson Intro- 

 duced hogs at about this same time, but they have not been observed 

 since and it is most likely that they have expired. One species of lizzard 

 is known from Socorro and It is the home of numerous sea and land birds. 



The vegetation apparently consists of two types determined by the 

 topography, soil, and the upland fogs; a maritime subtropical Thorn 

 Forest on the lower slopes and ridges and a maritime tropical montane 

 drought deciduous forest in the upper reaches of the canyons. Of the 

 brushy Thorn Forest, the ornithologist Anthony wrote (Auk II, 15 :312. 

 1898) ''The greater part of the island is covered with a very dense 

 growth of underbrush, the weather side [north and west exposure] 

 being especially thickly covered, making travel, except in favored spots, 



