June 21, 1907] 



SCIENCE 



967 



plain extends some ten miles seaward under 

 less than 100 feet of water. Above the sea 

 the plain is only five or six miles wide to 

 the base of the mountains. Kingston is situ- 

 ated on the side of a long narrow bay sepa- 

 rated from the sea by a beach ridge called the 

 Palisades, on the point of which is Port Royal. 

 A short distance east of Kingston the moun- 

 tains come to the sea, which suddenly deepens 

 to 500 feet within a half mile of the shore. 

 This is the head of an embayment in the mass 

 of submerged land, and plunges rapidly to a 

 depth of 4,000 feet. Beneath the limestones 

 mentioned are Pteropod oozes, which are ex- 

 ceedingly plastic when wet. The earthquake, 

 while felt over the island, was only intense 

 about King'ston, and still more so to the east 

 at the head of the submarine embayment men- 

 tioned. As this is the second great earth- 

 quake which has occurred here within recent 

 times, Mr. Spencer was inclined to regard this 

 local feature of the deep embayment as its 

 direct cause; and suggested that it might pos- 

 sibly be due to a gigantic submarine landslide 

 originating perhaps at a depth of 4,000 feet 

 or more. The land appears to have shifted 

 and part of the beach of Port Royal has 

 sunken beneath the sea, which is a repetition 

 of the features of the former earthquake. 

 While part of the possible submarine shift- 

 ing is due to this material, as at Port Royal, a 

 greater cause might be found in the move- 

 ment of the consolidated beds over the 

 Pteropod ooze similar to gigantic creeping 

 over similar beds in Barbados. 



Fred E. "Wright, 



Secretary 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 635th meeting was held on May 11, 

 1907. 



Mr. Becker read a paper on current theories 

 of slaty cleavage which will soon appear in 

 the American Journal of Science. The 

 speaker first mentioned very briefly the views 

 of various writers concerning the origin of 

 cleavage, but dwelt at some length upon the 

 theories of Sharpe, Van Hise and Leith. 

 Sharpe's theory was that cleavage is due to 

 pressure normal to the cleavage plane. Sedg- 



wick and others held cleavage mainly a phe- 

 nomenon due to crystallization or recrystalli- 

 zation of minerals in an appropriate orienta- 

 tion. Messrs. Van Hise and Leith have sought 

 to combine and amplify these theories. They 

 hold that minerals, especially mica, tend to 

 crystallize perpendicularly to the greatest 

 stress and also perpendicularly to the least 

 axis of the strain ellipsoid. 



Mr. Becker pointed out that the chances of 

 a pure strain, such as called for by Sharpe's 

 theory, are extremely small, not more than one 

 in 10,000 and probably much less. The sur- 

 faces perpendicular to the greatest internal 

 stress in a homogeneous mass subjected to 

 progressive uniformly distributed normal ex- 

 ternal pressure are the equipotentials and are 

 well known to be hyperboloids of revolution. 

 They are thus surfaces of double curvature 

 corresponding to no known phenomena in 

 slates. In the case of rotational strains the 

 equipotentials would be still more complex and 

 become intersecting systems of surfaces of 

 double curvature, and thus still less available 

 to explain cleavage. 



Mr. Becker took up one by one the lines of 

 evidence presented by Mr. Leith to establish 

 the position of the strain ellipsoid and the 

 hypothesis that the least axis is normal to the 

 cleavage. The elongation of pebbles is not 

 applicable to this purpose, for the final form 

 and attitude of a pebble result from the super- 

 position of the strain ellipsoid and the rotation 

 of the strain on the original ellipticities of the 

 pebble. Its elongation does not even tend to 

 coincide with that of the strain ellipsoid ex- 

 cepting in highly exceptional limiting cases. 

 Numerical examples were given showing that 

 pebbles of ordinary forms may be elongated in 

 directions 20° or 30° from the major axis of 

 the strain ellipsoid. Fossils as hitherto treat- 

 ed afford no better guide. 



Mr. Becker showed that the slicing of peb- 

 bles could be satisfactorily explained on the 

 theory that cleavage as well as jointing occurs 

 on planes of maximum slide. He rejected 

 Mr. Leith's inferences from the evidence and 

 concluded : 



It appears to me that Mr. Leith is in duty 

 bound to make public exact reasons for his asset- 



