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 derosiderites dis- 
play well-marked cleavage, usually octahedral (Toluca, 17, Henry 
Co., 136, Kenton Co. 134) but occasionally cubic (Braunau, 5%) 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 aerostderolites 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- 
crite. 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 derosiderolites pass so gradually from the derosiderites on the 
one hand to the derolites 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 derolites. - 
