Voiy. 6, 1920 
PETROLOGY: G. P. MERRILL 
463 
led me to regard the larger part if not all chondritic stones as originally 
tuffaceous and owing their more or less crystalline condition, where such 
exists, to heat and pressure in a nonoxidizing or even reducing atmosphere. 
The study of the origin of the chondritic meteorites must begin then with 
the study of the chondrules themselves as found in the tuffs and a gradual 
tracing of them back through the crystalline "kugelchen" forms to the 
holocrystalline types. 
Disregarding the fragmental, angular and more or less splintered radiate 
forms concerning the fracturing and secondary origin of which there can 
be no doubt, and confining ourselves to those which so far as can be de- 
termined have the form and structure assumed at the time of their formation 
and are of a more nearly perfect spherical, oval or "kugelchen" shape, their 
study in thin section brings out very clearly two important fundamental 
distinctions. 1st. The most perfectly spherical and oval forms, sharply 
differentiated from the matrix, are those showing a cryptocrystalline or 
radiating internal structure, and are mineralogically of pyroxene (en- 
statite or bronzite). These forms often show excrescences or saucer- 
shaped depressions, as through shrinkage or interference during solidi- 
fication. 2nd. Those of a polysomatic nature, composed of phenocrysts 
of olivine or pyroxene in a more or less glassy base, or of an almost holo- 
crystalline aggregate of one or more minerals, are of irregular outline, 
have more the appearance of fragments and never show the saucer-shaped 
depressions and excrescences. Further than this, it becomes very quickly 
evident that a theory of origin which will account for the first, must fail 
in the case of the second. It is not possible for instance, that a chondrule 
of phenocrysts in a glass base like that shown in figure 8, should 
have originated under the same conditions and in the same manner as 
that in figure 3. 
It is possible to conceive of a basic magma containing the necessary 
constituents for the formation of olivine or enstatite to be in a sufficiently 
liquid condition to cause, or allow it, when thrown into a hot or thin at- 
mosphere, to take the form of spherical drops which on cooling will become 
glassy or crystalline, according to conditions. Should the drop begin 
cooling on one point of its surface, the crystals might radiate from this 
point outward, or rather inward with reference to the chondrule, giving 
rise to the radiated form like those of the Elm Creek and Parnallee stones 
(figs. 3 and 5). In case the cooling began at several points on the 
surface, the interior of the chondrule would be broken into areas each of 
which represents an independent crystallization, as shown in figure 15. 
It would thus be fairly easy to account for the monosomatic glassy, crypto- 
crystalline and radiate forms'^^ (Kugels), and even the barred forms so 
characteristic of olivine chondrules in the stones of Henderson ville and 
'Tennasilm. 
The porphyritic polysomatic forms composed of phenocrysts of pyroxene 
