22 Field Columbian Museum — Geology, Vol. i. 



Other markings which may be noted upon the etched surfaces of 

 many irons are produced by included nodules of troilite. These may 

 take various forms, such as circular (Orange River,72, Allen Co. ,91), 

 oval (Staunton, 80), elongated (Toluca, 25), radiated (Hamilton Co., 

 131), or running in veins (Joe Wright Mountain, 121). 



Occasionally there appear upon the etched surfaces delicate, 

 short, sunken lines running in parallel directions or intersecting at 

 regular angles (Walker Co., 38, Maverick Co., 113, Hex River Mts., 

 115). According to Brezina these mark also the position of inclu- 

 sions of troilite. 



Other scattered, irregular flakes of a bronze-like lustre, indicate 

 the presence of schreibersite (Wichita Co., 41, Careyfort, 50, Youn- 

 degin, 118). 



Together with the crystalline structure • many aerosiderites dis- 

 play well-marked cleavage, usually octahedral (Toluca, 17, Henry 

 Co., 136, Kenton Co. 134) but occasionally cubic (Braunau, 55) or 

 dodecahedral. This structure is also possessed by some irons which 

 exhibit no etching figures whatever, and in general seems to be inde- 

 pendent of the crystalline planes because the cleavage planes fre- 

 quently pass through the crystalline plates, indicating that they are 

 of separate origin. 



The aerosiderolites consist usually of a spongy mass of nickelifer- 

 ous iron in the pores of which are contained grains of silicates. The 

 silicate most commonly found occurring in this way is chrysolite and 

 its typical mode of occurrence is shown in the Krasnojarsk (159) mete- 

 orite. This meteorite, having been first reported by the traveler 

 Pallas in 1776, is frequently known as the Pallas iron, and the name 

 Pallasite is given to meteorites of this class. Those of Kiowa Co.> 

 (200) are excellent examples. 



In the Rittersgriin meteorite, (164) the pores of the iron are 

 filled with a mixture of asmanite and bronzite, in that of Atacama 

 (170) with chrysolite mingled with pyroxene and chromite; in that of 

 Estherville (177) with chrysolite, diallage, pyrrhotite and troilite. 

 The aerosiderolites pass so gradually from the aerosiderites on the 

 one hand to the aerolites on the other that their grouping as a dis- 

 tinct class is adopted only for convenience. Occasionally, too, in indi- 

 viduals of the same fall, both classes are represented. Thus some 

 of the Kiowa Co. meteorites are true pallasites (200, 202, 206) while 

 others are entirely metallic(204,205). Among the stones of the Esther- 

 ville (175, 178) fall, can be traced every gradation between aerosidero- 

 lites and aerolites. 



