32 



GEOLOGY. 



never have had permanent atmospheres and hydrospheres. They 

 thus meet the requisite explanation of the absence of oxygen and water. 

 If built up by accretion, they should contain the requisite variety of 

 material, and, if formed in some other way, they might contain such 

 variety. In their different parts, they may present the required struc- 

 tural characteristics. The asteroids and satellites are undoubtedly 

 subject to deformations, attended by fractures, brecciation, veins, 

 slickensides and similar dynamic phenomena. Eruptive and explosive 



Fig. 10. — Section of the Brenham, Kans., meteorite, showing an intimate intermix- 

 ture of nickel-iron, the light-colored portion, and silicate and metallic com- 

 pounds, the dark portion. Ward-Coonley Collection. (From Ward.) 



action, as well as the impact of bodies falling from the exterior, may 

 have contributed the various forms of fragmental, amorphous, and 

 glassy material. The absence of a protecting atmosphere exposes 

 their surfaces to the full striking force of falling bodies, and also the 

 disrupting effects of extreme changes of temperature. On the exterior, 

 and at slight depths, amorphous material, as well as glassy and crypto- 

 crystalline rock, may have been formed. At greater depths, the vary- 

 ing conditions of pressure and temperature requisite for more complete 

 and coarser crystallization may have been possessed. The hydro- 



