452 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



compact lamellae of cohenite or schreibersite being repeatedly observed in the kamacite. Outcroppings of schreibers- 

 ite and graphite are sometimes combined in the same section in the most various ways, for example, pure graphite 

 to pure troilite, through various admixtures of the two, now in zonal superimposed stratification, again in juxtaposed 

 stratification, each one making a half lump, and again entirely mixed up; the lumps are frequently surrounded with 

 a corona of schreibersite; in one case a graphite-troilite grain with a corona of schreibersite forms the nucleus for the 

 upbuilding of a flat-faced schreibersite lamella 6 cm. long, parallel with the faces of an octahedron. Another section 

 shows a ball of troilite of the size of a mustard seed surrounded by a twofold substance with a high degree of luster, 

 and consisting apparently of cohenite and schreibersite, which is bordered on the outside, next to the kamacite, with 

 a crystalline material. 



Another section which is cut diagonally through a round, flat, smooth protuberance on the natural exterior of a 

 fragment, shows upon etching the undisturbed penetration of the Trias into the protuberance. The gradual dissolving 

 of large masses of the Toluca iron gives frequently very regular crystals or fragments of crystals of schreibersite. The 

 sawed section, oriented occording to the faces of a cube gives large tsenite skeletons, on which the peculiar structure, 

 the alternate preponderance of the one and the other octahedron in the development of the laminae, may be very 

 readily followed. Two specimens recently received by the Vienna museum, one designated as Zacatecas and the 

 other in Baumhauer's collection, without indication of locality, both undoubtedly belong to Toluca. The latter shows 

 long, straight, hatched, somewhat swollen bands 0.8 mm. wide; kamacite granular, slightly hatched, with numerous 

 etching pits; fields gray, and full of combs; taenite well developed, especially on the swollen ends, as a triangular 

 filling. Rhabdite is abundant in this specimem also. It has great similarity with that of Hacienda Mani. A piece 

 of the latter shows the kamacite granular as in Carthage, but not hatched. 



Cohen 37 found Toluca irons capable of acquiring strong, permanent magnetism. The 

 teenite he found to easily acquire permanent magnetism, to show no marked change on heating, 

 and to retain the magnetism a considerable time. The cohenite and schreibersite were less easily 

 magnetized and lost their magnetism quicker. No polar magnetism could be observed on the 

 tsenite of Toluca. 



The specific gravity of specimens of the Toluca iron he found to be 7.794 at 15.8° C; of 

 the schreibersite, 7.1118 at 18.8° C; and of the tsenite, 7.6122 at 17.6°. On exhausting the 

 air from the tsenite different values for the specific gravity were obtained. Thus when the air 

 was not at all exhausted the value found was 6.8; on exhausting 2 hours, 7.5022; and on 

 exhausting 4 hours, 7.6122. Thus a lamellar structure of the tsenite is indicated. 



Cohen 38 gave the following account of a study of some apparent cohenite crystals in 

 Toluca : 



On one end of a section of Toluca iron in the collection of the University of Freiberg, in immediate connection 

 with the original, rust-covered surface, occur large numbers of crystals in kamacite, which, according to their physical 

 characteristics and appearance, correspond with the crystals of cohenite in Magura, Wichita, and Beaconsfield. Since 

 neither this series of accessory ingredients nor the presence of cohenite in Toluca iron was known to me, I isolated 

 with dilute hydrochloric acid a few crystals, which from their appearance seemed to be of exactly the same sort. 

 Contrary to expectation, I found one portion to consist of cohenite and another part of schreibersite. From which it 

 appears that these two minerals can not be differentiated with certainty either by their physical characteristics or the 

 manner of their occurrence. 



Cohen 39 gave a further description of a specimen of Toluca, as follows: 



I received as a gift from Dr. Naumann a gift of a rust-covered specimen of the Toluca iron weighing 1,700 grams, 

 the etched section of which gives so complete an agreement with numerous specimens of the Toluca iron as to make 

 the determination of the locality of the mass under consideration quite certain, but it shows sufficient difference in 

 the finer structure of the bands to call for brief description. 



While in general, extensive and deep hatching, accompanied by comparatively large and deep etching pits, may 

 be regarded as especially characteristic of the kamacite of the Toluca irons, yet in this case both the hatching and 

 etching pits are very inconspicuous. On the first two sections, which were cut from one end of the elongated meteor- 

 ite, they are entirely wanting; on the next two sections they are scarce, being either confined to individual bands or 

 neither so numerous nor so deep as in normal Toluca iron. Instead, the bands are spotted, usually without but some- 

 times with granulation; especially in the former case the spots appear indistinctly defined. The oriented sheen is 

 very marked, and the taenite fully developed, as is usually the case. 



From these four sections it is apparently possible that the interior of the mass has the normal structure; but I 

 did not consider proof of this of sufficient importance to warrant cutting the mass through the center. No evidence 

 of an altered zone is furnished by the section under consideration, which is a complete cross section almost 4 cm. thick, 

 having the same appearance in the central portion as at the borders. 



Brezina has frequently observed a like abnormal development of Toluca iron. He mentions a piece from the 

 Baumhauer collection with granular slightly-hatched kamacite; from the Hacienda Mani, a granular kamacite, com- 

 parable to that of Carthage; and, according to a brief communication, there is a section in the collection of the Mar- 



