146 CARNEGIE INSTITUTION OF WASHINGTON. 



it neglects the rotation of the plane of vibration of transmitted plane-polarized 

 light waves at all boundary surfaces both of crystal plate and of microscope 

 lens system ; that of the writer because of similar neglect of the rotation of the 

 vibration plane by the lens system. It shows, furthermore, that because of 

 this rotation a theoretically correct method is not possible. For practical 

 purposes both methods furnish results of about the same order of accuracy. 



(508) On the nomenclature of the point groups. Ralph W. G. Wyckoff. Am. J. Sci., 



6, 288-290. 1923. 



The desirability of changing the prevailing point- and space-group nomen- 

 clature is mentioned and a system proposed which is a modification of that of 

 Hilton. 



(509) Stone adzes of Egypt and Hawaii. Henry S. Washington. J. Wash. Acad. Sci., 13, 



377-383. 1923. 



The attention of anthropologists is called to the remarkable similarity in 

 form between the stone adzes used, about 2500 b. c, to excavate (out of lime- 

 stone) the tomb-chambers at Beni Hassan, on the east bank of the Nile, and 

 those used by the Hawaiians, as late as 1864, for felling trees and shaping 

 wooden canoes and idols. The Egyptian adzes are made of a hard, dense 

 sihceous limestone, composed of secondary silica and calcite in about equal 

 amounts, whereas the Hawaiian adzes are made of a very dense, fine-grained 

 basalt, which occurs at only a few places on the islands. The resemblances 

 consist in the general size and shape of the tool, the curvatures of the faces 

 that make the cutting edge, and the angle of this. Although it is possible that 

 the Polynesian form was derived from the Egyptian through ancient lines of 

 trade, yet the writer believes that the two were of independent origin and 

 arose from similar solutions of similar problems. 



(510) Petrology of the Hawaiian Islands: IV. The formation of aa and pahoehoe. Henry 



S. Washington. Am. J. Sci., 6, 409-423. 1923. 



The two most common types of basaltic lavas at the Hawaiian and many 

 other volcanoes are usually called by their Hawaiian names, "aa" and 

 "pahoehoe." The former, also called "block lava," forms long, thick flows, 

 with extremely rough surfaces made up of very irregular, jagged blocks, with 

 more solid rock below. Pahoehoe is a "ropy lava," usually in shorter and 

 thinner flows, formed of coils, festoons, ropes, and lobes, with smooth, glisten- 

 ing surfaces. Internally, aa contains rather few but large and irregular gas- 

 vesicles, whereas pahoehoe has very numerous, small, and mostly spherical 

 vesicles, uniformly distributed. The cause of these differences has for long 

 been in doubt, and this paper records an attempt to solve the problem through 

 chemical analyses and study of thin sections of many Hawaiian basalts. 



Analyses show that the two types are chemically identical, except that the 

 ratio of ferrous to ferric oxide is slightly greater in pahoehoe than in aa. As 

 the microscopic study shows that pahoehoe is always more glassy than aa, 

 this difference in the iron oxides is connected with the general rule that the 

 more glassy the texture of a lava the higher the ratio of ferrous to ferric oxide, 

 the chemical composition being otherwise the same; so that this chemical 

 difference has nothing to do with the physical differences. The general ex- 

 planation of the differences between the two types is as follows. 



Pahoehoe lava issues at a higher temperature than aa and has lost much 

 of its magmatic gas by simmering in the throat of the volcano; it also contains 

 very few or no crystals when it reaches the surface. As it contains little gas, 

 the presence of which in solution would increase the fluidity, pahoehoe is 

 rather viscous and solidifies rapidly, although it remains for some time suf- 

 ficiently liquid or semi-liquid to permit of slow movement of the mass as a 



