186 



ANNUAL REPOET SMITHSONIAN INSTITUTION, 1917. 



pronounced example of the friable kugel chondritic type. These 

 were substantially as follow^: 



The general structure of the Allegan stone can, I believe, be ac- 

 counted for only by regarding it as an agglomerate of chondrules 

 embedded in a fragmental ground mass or matrix, the materials of 

 which were derived from the trituration of other chondrules. Ob- 

 viously, if the stone is a product of crystallization in mass, the 

 chondrule3 are the products of the earliest cooling and, judged by the 

 standards of terrestrial petrography, should be the most highly crys- 

 talline, while the base in which they are embedded might be glassy 

 or crystalline, according to conditions. In reality the reverse is the 

 case, and, so far as I have observed, there is never any true glassy 

 base in metorites of this type. The subject of the spherules in lipa- 

 rites has been pretty thoroughly worked out by Cross and Iddings ; 

 and while it is easy to conceive of the abrupt transition from a wholly 



or partially crystalline spherule to a 

 glassy base, as sometimes seen in spheru- 

 litic rocks, it will, in the present condi- 

 tion of knowledge, puzzle any petrog- 

 rapher to account for an equally sharp 

 transition from a glassy spherule (chon- 

 drule) to a base composed wholly of 

 crystalline particles, as shown in many 

 meteorites. Even could we account for 

 such anomalies of crystallization, the 

 presence of fragmental chondrules, of 

 chondrules which were fragments at the 

 time of the final consolidation of the stone, 

 would yet remain to be explained. The forms shown in figure 4 were all 

 carefully picked from the rock without crushing. That they are origi- 

 nal fragments, i. e., not due to fracturing in place, is shown by the dull, 

 lusterless character of the surface of fracture, and, further, by the fact 

 that in no case was the remainder of the chondrule represented by one 

 of these pieces found in the vicinity. No. 1, in figure 4, represents a 

 complete chondrule, No. 2 one but slightly corroded, while the others 

 are plainly fragmental. No. 5 i3 one of the most striking illustra- 

 tions, being that portion of an enstatite chondrule, some 8 milli- 

 meters in diameter, embedded in a fine clastic ground. The flat 

 surface of fracture is unquestionably an old one. No. 6 shows a 

 side view of the same chondrule. In other cases as in 3 and 4 the 

 fractures are old and show abraded surfaces. Nos. 2 and 5 are 

 plainly those of elongated chondrules that have been broken across. 

 No. 1 is a peculiarly suggestive form having the appearance of a 

 once molten globule which, on cooling, contracted, producing the 

 concavity shown. Such forms lend support to an idea advanced 



Fig. 4. — Chondrules from 

 Allegan meteorite. 



