180 prof. w. j. sollas on [May 1903, 



16. T7i<3 Figure of the Earth. By William Johnson Sollas, M.A., 

 D.Sc, LL.D., E.B.S., F.G.S., Professor of Geology in the 

 University of Oxford. (Read January 21st, 1903.) 



Some of the more striking features of our planet are apt to escape 

 attention if our studies are made upon charts without the assistance 

 of a ' globe.' Thus the remarkable alignment of many volcanoes, 

 volcanic islands, coast-lines, and even mountain-chains along circular 

 arcs does not seem to have excited the interest which might 

 otherwise have been expected. An arc-like form is not infrequently 

 alluded to, but the almost precise correspondence of some great 

 terrestrial features with a circular form seems to be generally 

 overlooked. As an example, the chain of the Aleutian Islands may 

 be cited : it is certainly one of the most perfect. If a circle be swept 

 out on a terrestrial globe with its centre in lat. 6° N., long. 177° W., 

 its circumference passing through one of the islands of the festoon 

 will traverse nearly all the rest and extend through the length of the 

 Alaskan peninsula. (See Al in fig. 2, p. 183.) The correspondence 

 is so precise as to suggest that it must have some real physical 

 meaning. The numerous mighty volcanoes which characterize the 

 region point to the existence of an extensive subterranean reservoir 

 of lava, and to discontinuity of the earth's crust, in the form of a 

 circular crack. It is difficult, as we look upon this part of the globe, 

 to avoid the impression that we have before us the remains of a 

 spherical dome or blister, which has broken down along circular 

 and radial fractures, the islands standing over a circle, the coasts 

 of the Kamchatkan Sea marking irregular radial splits. Deep sea 

 exists outside, not far removed from a region regarded by Prof. Milne 

 as the origin of many of the earthquakes which shake the whole 

 crust of the earth. 



The East Indies present another, almost equally close corre- 

 spondence, but on a much grander scale. The centre of this arc is 

 situated about 15° lat. N., 118° long. E., immediately west of the 

 island of Luzon : the arc itself commences in Burmah, and con- 

 tinues past the Andaman Islands, the extremity of which it just 

 touches, extends then through the Sunda Islands, grazes Java, 

 traverses Jindana and the north of Timor, and finally passes 

 parallel to the north-western coast of New Guinea and to the Ladrones, 

 which lie somewhat to the east. Numerous smaller circles may be 

 drawn concentric with this, showing a remarkable correspondence 

 with the trend of the islands and coast-lines of the region. 



The sudden inflexion of the Malayan arc off Timor Laut through 

 the Banda Isles is an interesting discordance, not without parallel, 

 and will be alluded to later. The leading features of the islands 

 which correspond more or less, not to a peripheral, but to a radial 

 direction, do not strictly follow the radii of the circle, but are often 

 curves and more or less excentric, while some, like that ending in 



