VIEWS OF PROFESSOR B. BALFOUR. 307 
which, when it reaches the surface, reclaims, so to speak, 
the space inside it, which is soon filled up with sand and 
veei-debris. The evidence, in fact, goes to show that a 
reef grows seaw T ard rather by jumps than by a gradual 
outward growth. This inference is of considerable import- 
ance since it connects all classes of reefs together in the 
matter of their seaward growth, the degree of inclination 
of the submarine slope being the chief determining factor.’ 
Proceeding now to the papers favourable to Mr. Darwin’s 
views we may quote first a passage in Professor Bayley 
Balfour’s description of the physical features of Rodriguez 1 
which has an important bearing on one point in recent 
controversies. After stating that the island is substantially 
a hilly mass of volcanic rock, the highest point being 
1,300 feet above sea level ; that the western slopes of this 
terminate in a wide coralline limestone plain, diversified 
with elevations ; and that a fringing reef of coral, studded 
with islets, skirts the island on every side, extending on 
the west about three miles from land, but with its edge at 
the eastern end within about one hundred yards of the 
beach ; he proceeds : — ‘ On the south-west the central vol- 
canic ridge gradually descends, the ravines become less 
deep, and the ground spreads out into a large coralline 
limestone plain. The demarcation betwixt the limestone 
and the volcanic rock is very sharp, but isolated patches of 
limestone are met with on the surface of the volcanic 
region in the vicinity of the main mass. . . . The lime- 
stone is not found along the northern or southern shores, 
until we near the eastern extremity, where patches occur 
at the mouths of valleys, and even at some distance from 
the shore. . . . On the southern shore between Riviere 
Palmiste and Riviere Poursuite, indications of raised 
beaches are seen, reaching about 20 feet above the sea 
1 Philosoph. Transact. R. S. vol. clxviii. (1879), p. 289. 
