METEORITES OF NORTH AMERICA. 203 



The large amount of chlorine in the rust coating (4.99 per cent), in comparison with the small amount in unaltered 

 nickel-iron (0.17 per cent), is explainable as a result of diffusion, and the strength of the same is governed by the 

 greater or less porosity of the nickel-iron. That the latter, in the case of Forsyth, is particularly strong would be 

 inferred on account of the conspicuously low specific gravity. 



As to the origin of the two varieties of structure: Since the chemical composition of both varieties is the same, 

 the manner of the cooling of the iron can alone be assumed as the cause of the structural differences; accordingly, the 

 granular structure must have been the central, slower cooled portion of the meteorite, the dense or amorphous portion 

 the peripheral mass. If this is actually the case, the very irregular border running along with the present exterior 

 surface would indicate that the meteorite originally had a very different form, and that a flaking off had taken place, 

 which separated the densely constituted portion on the one end of the block. This would also explain why the acces- 

 sory masses of troilite and graphite lie preferably in the dense portion, since they usually predominate in the 

 peripheral portion of iron meteorites. Moreover, the form as indicated by the figure submitted by de Schweinitz 

 does not militate against the assumption that a splitting off of portions of the mass took place. 



The specific magnetism of a granular portion was determined by Leick as 0.21; of a compact portion as 0.57, and 

 of a partly granular, partly compact piece as 0.17 absolute units per gram. The permanent magnetism of all three 

 pieces was very weak. 



BIBLIOGRAPHY. 



1. 1896: de SCHWEDJTTZ. A meteorite from Forsyth County, North Carolina. Amer. Joum. Sci., 4th ser., vol. 1, 



p. 208. 



2. 1897: COHEN. Das Meteoreisen von Forsyth County, Georgia. Sitzber. Berlin Akad., 1897, pp. 386-396. 



3. 1905: COHEN. Meteoritenkunde, Heft 3, pp. 74-79. 



FORT DUNCAN. 



Maverick County, Texas. 



Latitude 28 35' N., longitude 100 24' W. 



Normal hexahedrite (H). of Brezina. 



Under the name of Fort Duncan Brezina and Cohen group the following: 



1. Sanchez (Sancha) estate, Coahuila, Mexico. (Also called Saltillo, Couch, Cauch, or 



Gouch.) Iron, found 1850, weight 114.33 kgs. (231.5 Ibs.). 



2. Smithsonian iron ("locality unknown" in many catalogues). Described 1881, weight 



3,638 gr. (8 Ibs.). 



3. Fort Duncan, Maverick County, Texas. Found 1882; described 1886; weight 43.5 kgs. 



(96 Iba.). 



Here also, according to Brezina, a small specimen of the Vienna collection which Jackson sent 

 under the designation: "Taos. New Mexico, Sierra Blanca, N. Santa F, 144 km. south of 

 the Gila River." 



The history and characters of these meteorites are summarized by Cohen " as follows : 



Sanchez Estate. According to the data from Lieutenant Couch the mass at Saltillo was used as an anvil, but origi- 

 nated from Hacienda Sanchez (Sanchez Estate\ 50 to 60 miles from Santa Rosa in the north of Coahuila, where several 

 other iron masses of considerable dimensions have been found. When the mass reached the Smithsonian Institution 

 it weighed 114.25 kgs. (252 Ibs.), although Smith 2 concluded from the presence of plane boundary surfaces that it was 

 originally heavier. According to the illustration furnished by Smith its form is cylindrical with projecting points, 

 saucerlike pittings seeming to be wanting. The exterior shows only slight traces of chlorine. The iron is malleable 

 and not hard to cut and gives an etching surface similar to that of Braunau. After treatment with hydrochloric acid 

 finely divided schreibersite remains behind in brightly glistening flakes. Other minor constituents were not observed. 



According to Fletcher, 13 Genth's analysis ! of a specimen, for which New Mexico was erroneously given as the 

 locality, belongs to the same iron (Sanchez Estate). Rose * observed on this supposed New Mexico iron etching lines 

 and rhabdite. 



Burkart 4 left it uncertain whether Sanchez belonged to Coahuila, but considered it probable. Brezina 18 iden- 

 tified it with Fort Duncan and cited the abundance of rhabdite, which on the one hand is evenly distributed through 

 the entire mass, on the other hand in especially large examples is crowded together in long parallel layers, surrounded 

 by a common etching area. 



Fletcher I3 thinks that the mass may have been brought to Saltillo by way of Santa Rosa to be used as an anvil, 

 and that the Hacienda Sanchez lies north from Santa Rosa where the Bonanza iron was found. If Coahuila and Fort 

 Duncan, including Sanchez Estate, are considered different irons Fletcher's view would naturally be incorrect. Hunt- 

 ington 9 determined the specific gravity of five different pieces and obtained values from 7.631 to 7.925, which led him 

 to conclude that the material was not uniform. Further, according to him, Sanchez as well as Duncan, in contrast to 

 Coahuila. show complete cubic cleavage and large cleavage planes are distinguished by lack of striations and by a scaly 

 appearance such as is characteristic of many alloys. A small section which I received from the Gregory collection under 

 the name of Saltillo shows abundant etching lines, regular distribution of rhabdite, and marked resistance to acid. 



