948 



SCIENCE 



[N. S. Vol. XXIX. No. 754 



of the former precipitous peak and the slide 

 may have been brought about by some, if not 

 most, of the following contributory causes: (1) 

 the massive limestones forming the upper two 

 thirds of the mountain had been thrust out over 

 the underlying softer shales and sandstones, and 

 therefore may have been in a state of more or less 

 unstable equilibrium; (2) a considerable layer 

 at the base of the massive limestones had been 

 brecciated by the thrust faulting and had thus 

 lost its homogeneity and competency; (3) the 

 limestones forming the upper part of the moun- 

 tain were very massive and thus more liable to 

 accumulate strain and to give way in a body than 

 would have been the case with weaker rocks; and 

 (4) the opening up of so thick a coal seam, to 

 such a height and for so long a distance in a 

 direction perpendicular to the dip of the massive 

 overlying beds, in rocks incompetent to withstand 

 the pressure thus induced, created strains in the 

 massive rocks from which the support had been 

 removed. 



Philip S. Smith, 



Secretary 



At the 217th meeting of the society, held at 

 the Ck)smos Club on Wednesday evening, March 

 24, 1909, under informal communications, Dr. J. 

 W. Spencer presented briefly some notes on the 

 " Recent Draining of Niagara Falls." 



Regular Program 

 The Composition of Stony Meteorites: Geo. P. 



Mebrill. 



The average of a large number of analyses of 

 stony meteorites shows close agreement, after the 

 elimination of the metallic iron, with terrestrial 

 peridotites. From a magma of this kind no 

 amount of magmatie differentiation could produce 

 a series of rocks as rich in silica, alumina, lime 

 and alkalies as those shown by the averages cal- 

 culated by Clarke and Washington to be charac- 

 teristic of the earth's crust. World origin through 

 the segregation of materials of this nature is 

 therefore impossible. At the same time it may 

 be conceived that the relative proportion of the 

 elements which make up the mineral matter in 

 the various bodies wandering in remote space, 

 varies widely. If this is so, the earth to-day, in 

 its course, may be passing through and receiving 

 from space deposits of material representing one 

 and the same original body, but not necessarily 

 resembling, in percentage composition, the ma- 

 terials which reached it during past and earlier 



stages of the earth's history. In brief, the stony 

 meteorites may be regarded as products of an 

 extremely basic phase of magmatie differentiation 

 from a previously more acid magma. 

 Chemical Composition as a Criterion in Identi- 

 fying Metamorphosed Sediments: E. S. Bastin. 

 Chemical criteria need seldom be resorted to for 

 the identification of metamorphosed sediments of 

 a highly siliceous or a highly calcareous nature. 

 They are inapplicable for the identification of 

 many of the metamorphic equivalents of the 

 arkoses, greywaekes and similar rocks, since these 

 may be almost identical in composition with the 

 igneous rocks from which they have been derived. 

 Chemical criteria are also inapplicable in the 

 recognition of flow gneisses and of injection 

 gneisses. Such criteria are therefore restricted 

 in their usefulness for the most part to the differ- 

 entiation of metamorphosed equivalents of the 

 argillaceous sediments from metamorphosed plu- 

 tonic and volcanic rocks. 



The available analyses of metamorphosed igne- 

 ous rocks show that well-developed foliated struc- 

 tures may in many cases be developed without 

 important chemical changes, and it seems prob- 

 able that in a very large number, if not in most, 

 of the metamorphosed igneous rocks with which 

 the geologist has to deal the chemical changes 

 during metamorphism have not been severe enough 

 to obscure their igneous characters. They are in 

 many instances still igneous rocks in composition, 

 and the chemical criteria for distinguishing them 

 from metamorphosed sediments may be brought 

 out by a comparison of the latter with normal 

 igneous rocks as tabulated in Washington's tables 

 of analyses. 



The chemical characteristics of the argillaceous 

 sediments and the changes they undergo during 

 metamorphism may be determined by a compari- 

 son of the averages of a large number of analyses 

 of clays, shales, slates and schists. By comparing 

 these sedimentary averages with the igneous rocks 

 as tabulated in Washington's tables of rock an- 

 alyses, the following chemical characteristics are 

 shown to be suggestive of sedimentary origin. 



1. Excess of alumina (AljOs) above the amount 

 necessary to satisfy the ratio of 1 to 1 with which 

 it is normally combined with lime and alkalies in 

 igneous rocks. 



2. Excess of magnesia over lime (MgO > CaO). 



3. Excess of potash over soda (K^O > NajO). 



4. In some instances, excess of silica (SiOj) has 

 confirmatory critical value. 



The evidence of sedimentary origin is greatly 



