280 HOBBS— THE EVOLUTION AND THE [April 24, 



built up on radial fissures going out from the ruptured center of a 

 depressed area, reveal a regular plan with the volcanic peaks and 

 craters at the crossing points of intersecting lines, so soon as the 

 submerged cones are brought into the problem (see Fig. 3).^^ The 

 volcanoes of Italy and surrounding waters furnish an example of 

 a much larger network within which the vents are located at inter- 

 secting points.^*' 



What is true of the arrangement of ordinary volcanic cones 

 within individual provinces, is repeated in the case of the monti- 

 cules or parasitic cones which are built up upon the flanks of larger 

 composite volcanoes, such, for example, as Etna.^^ To some extent 

 a similar arrangement may be inferred on a far grander scale than 

 any that has been mentioned, as in the longer trains of the volcanic 

 islands. As long since pointed out by Neumayr, the volcanic island, 

 St. Helena, is located at the crossing point of two long lines of 

 widely separated volcanoes, one trending NE.-SW., and the other 

 NW.-SE. (See Fig. 4). One of these, the well known " Cameroon 

 fissure," bisects the Gulf of Guinea and includes the volcanic islands, 

 St. Helena, Annobom, Sao Thome, I. do Principe, and Fernando Po. 

 On the land this fissure is continued in a striking manner by the fault 

 bridge which ends in the Tschebitschi, 2,000 meters high, which then 

 drops suddenly to the level of a low plain less than 200 meters above 

 the sea. The volcanotectonic line which intersects this striking 

 lineament at St. Helena, includes Ascension, one of the eastern cones 

 of St. Paul's Rocks and a conical, submerged elevation upon the 

 sea floor, almost under the tropic of Capricorn about 800 kilometers 

 southwest of Amboland. 



In addition to these two fissure directions, a third is like them 

 strikingly characteristic of the African continent, as shown by the 

 remarkable north and south lines of volcanoes and rift valleys in 

 central Africa east of the Nile. To these three prevailing directions, 

 northwest-southeast, northeast-southwest, and north-south, must be 

 added a fourth less common direction, namely, east-west. Simmer 



**Hobbs, Gerlands Bcitrage z. Geophysik, Vol. 8, 1907, pp. 316-317. 

 ""Ibid., pp. 315-316, smaller map of pi. 3. See also Suess, "The Face 

 of the Earth," Vol. i, p. 144. 



" Hobbs, /. c, pp. 348-349, pi. 10. 



