38 WILLIAM H. PICKERING 
weakness; and when the flow of steam and viscous rock from below 
on all sides toward the area of diminished pressure again increases 
this pressure beyond the breaking strength of the resisting material, 
the eruption will be renewed. 
Volcanoes frequently lie along arcs of circles, which, if complete, 
would resemble the lunar maria both in size and shape. One of 
the most complete of these series of arcs has the China Sea for its 
center, while the volcanoes are found in the Philippines, Celebes, 
Java, Sumatra, the Malay peninsula, and southern China to the 
west of Canton. The diameter of this circle is 2,000 miles. The 
Japan and Bering Seas are similarly partly surrounded by incom- 
plete arcs. The shape of the latter is decidedly elliptical. 
