55° STUDIES FOR STUDENTS 



EXPLANATION OF PLATE IV 



Fig. i. — Samples of brown sandstone in which the pyramidal 

 forms are well developed. 



Figs. 2 and 3. — Samples of granite. Only the upper wedge or 

 pyramid was developed in each cube. Fig. 2 approaches the conical 

 form, which ordinarily results from crushing granite. (See PI. II.) 

 Fig. 3 is the typical wedge-shaped form, which often results from 

 crushing granite of medium strength. 



Fig. 4. — Samples of brown sandstone in which the pyramidal 

 structure is well developed. These are typical results obtained from 

 crushing sandstone of ordinary strength. It should be observed that 

 the samples which have a low or medium crushing istrength are the 

 only ones in which two equally well developed pyramids occur. 



