470 G. P. Merrill — Composition of Stony Meteorites. 



individual members. It is obvious, however, that whatever 

 theory is adopted, — the Laplacean, meteoric, or the planetesi- 

 mal — the kind of material, and presumably the ultimate origin 

 of all, remains the same. It is this thought which has led me 

 to enter upon the present discussion. 



Meteorites as they come to our earth, as is well known, are 

 roughly grouped into three general classes ; first, those which 

 consist essentially of nickeliferous iron nearly or quite devoid 

 of silicate material ; second, those which consist of a spongy 

 mass of iron, including globular aggregates of silicates ; and 

 third, those which are nearly or quite all of silicate material, 

 with more or less sporadic iron. These forms, it is true, grade 

 into one another, but, nevertheless, the classification is much 

 easier than one would be at first led to suppose. 



Researches into the composition of our earth have led us to 

 assume that it is composed of an outer zone of comparatively 

 rich silicate material, in which free silica is an important con- 

 stituent, and an inner zone of material which is essentially 

 metallic, with perhaps an intermediate zone showing a transi- 

 tion between the two extremes. Regarding meteorites as 

 world materials, as has been done by certain workers, we 

 might consider the purely metallic varieties as representing the 

 deep-seated, probably nucleal, material of some pre-existing 

 planetary body ; the stony meteorites as representing the 

 crustal material ; and the spongy irons with the mixed silicates 

 (pallasites) as representing the intermediate portion. The 

 fact, however, that a part, at least, of the iron of stony mete- 

 orites has been repeatedly shown to be of secondary origin — 

 to result from the reduction of some compound subsequent to 

 the consolidation of the silicates, is difficult to harmonize with 

 any such view. 



Inasmuch as the nucleal material of the earth is quite beyond 

 reach for purposes of investigation, and as the intermediate 

 zone, if such there be, is represented, if at all, only by extrusions 

 of deep-seated igneous rocks, I have for the time being limited 

 my considerations to a comparison of the stony meteorites 

 with the great group of igneous rocks as existing to-day upon 

 the earth's surface. It will be seen at once that in doing this, 

 I have accepted for the purpose the most acid group of the 

 ultra-terrestrial rocks. 



There are many difficulties in the way of obtaining anything 

 like an accurate average of the composition of these materials. 

 This, for reasons which can be fully appreciated only by those 

 who have attempted their study, and more particularly, the 

 making of chemical analyses. One of the chief difficulties, it 

 may be said, lies in the separation of the metallic from the 

 non-metallic portion. The method of statement of the results, 



