GEOLOGY IN NATIONAL MUSEUM — MERRILL. 285 



the finely contorted shale (Nos. 83862 and 75535) from Maryland. 

 In cases where the earth stresses have been sufficiently great, or the 

 rocks through composition or lack of load were too brittle, crush- 

 ing and fracturing with more or less displacement ensued, produc- 

 ing what are known as faults. In some instances the amount of 

 displacement was so slight that examples can be shown by speci- 

 mens as in the faulted sandstone, from South Dakota or the gneiss 

 from Montana. The slate showing cleavage and faulting (fig. 3, 

 pi. 12) is especially instructive. 



METEORITES. 



The collection of meteorites, occupying special bases and cases 

 in the center and on the west side of the hall, comprise the C. IT. 

 Shepard collection, numbering 234 falls and finds, and that of the 

 Museum proper numbering 407 falls and finds. The collections par- 

 tially duplicate one another, but collectively represent 496 independ- 

 ent falls and finds. 



Below is a transcript of the general label accompanying the col- 

 lection : 



Metkoeites : Sky Stokes. 



The term meteorite is applied to those bodies of stone or 

 metal which occasionally fall to the earth from space. Such 

 are composed sometimes almost wholly of metal or, again, 

 of stony matter, with many intergradations. The metal is 

 mainly iron alloyed with nickel and cobalt ; the stony matter 

 mainly olivine and pyroxene with more rarely feldspar and 

 free silica in the form known as asmanite. Other minerals 

 in minor proportions are the phosphide of iron, schreibersite 

 ( rhabdite ) ; the oxide of iron and chromium, chromite ; the 

 sulphides of iron, troilite or pyrrhotite; the chloride of iron, 

 lawrencite; the last named, on account of its ready oxidation 

 in a moist atmosphere, producing the rusty appearance and 

 even disintegration of many meteorites and necessitating 

 their preservation in a petroleum distillate or other medium. 

 According to the proportional quantities of the metallic and 

 silicate constituents, the meteorites fall into three general 

 groups, with intermediate gradations. These three are (I) 

 Meteoric irons, or siderites ; (II) meteoric stony irons, or 

 siderolites; and (III) meteoric stones, or aerolites. Sub- 

 divisions of these groups are based on minor distinctions. 



The exhibition begins with an introductory series showing each 

 of the principal types, and examples of etched irons with Widman- 

 statten figures and other markings ; there are also separations of troilite 

 nodules, chondrules, schreibersite, cohenite, carbon, etc. Through the 

 center of the hall are displayed on special bases (pi. 15, fig. 1) the 

 larger metallic masses of Tucson, Casas Grandes, Canon Diablo, and 

 Owens Valley, while in special cases between the columns are the 



