468 
PETROLOGY: G. P. MERRILL 
Proc. N. a. S. 
original forms were spheroidal or that of an ordinary angular fragment 
there is no absolute means of determining. From the examination of a 
large number of cases, I am inclined to the belief that these last are 
altogether of fragmental origin, broken fragments rounded by mechanical 
action. 
From a lot of disintegrated Bjurbole material, generously furnished 
by Dr. J. J. Sederholm, there were in like manner picked out the two 
series shown in figures 5 and 8, pi. 1. It will be noted here that there is a 
greater contrast between the two forms than in the case of Allegan. Those 
in figure 5 are typical blebs of fiery rain, smooth, with a rind-like coating 
showing frequent depressions and more rarely excrescences. A large 
number of like forms were broken with a hammer and yielded smooth, 
cleavage-like fractures in part with a radiate structure. In thin sections 
all showed either a dense cryptocrystalline or radiate internal structure 
(figs. 6 and 7). 
The forms shown in figure 8 were, as in the case of Allegan also, less sym- 
metrically oval or spherical, rough exteriorly, never encrusted or showing 
depressions or excrescences. On breaking with a hammer some of these 
yielded a smooth, straight, cleavage-like fracture and in the section showed 
a radiate structure; others and the larger part showed an uneven fracture 
and in the section were irregularly granular, glassy and porphyritic (figs. 
9 and 10). 
I find a similar, though not always so plainly marked, distinction in the 
chondrules separated out from the meteorites of Ochansk, San Emigdio 
and Soko Banjo. A further study of a large number of sections of chon- 
dritic stones fully confirms these observations. Stated in brief the con- 
ditions and conclusions are as follows: 
(1) Only the chondrules of glass and cryptocrystalline or radiating 
enstatites (kugelchen) present the rounded or oval form with smooth 
rind-like crust and surfaces, with often one or more saucer-like depressions 
or excrescences such as are consistent with a theory of origin as fused 
drops of "fiery rain" (Sorby). 
(2) Chondrules of a compound, holocrystalline nature, and those 
porphyritic through the development of olivine or pyroxene phenocrysts. 
in a more or less glassy base are lacking in smooth exteriors and though 
often quite spherical in outline, are as a rule more or less irregular and 
in many instances show unmistakable evidences of an origin of form 
through mechanical attrition. These distinctions are well shown in figures 
3 and 5, and in the general view from a thin section of the stone of 
Cedar, Texas (p. 462). 
Many of the irregular forms, it is true, are found to be of the radiating 
or cryptocrystalline enstatite. This is evident from an examination of 
