CHAPTER VI 



THE ARCHITECTURE OF THE FRACTURED SUPER- 

 STRUCTURE 



The system of the fractures. In referring to experiments made 

 upon the fracture of solid blocks under compression (p. 41), it was 

 shown that two series of parallel fractures develop perpendicular 

 to each free surface of 

 the block, and that 

 these series are each of 

 them inclined by half 

 of a right angle to the 

 direction of compres- 

 sion, and thus perpen- 

 dicular to each other. 

 The fragments into 

 which a block with one 

 free surface would thus 

 tend tQ be divided 

 should be square prisms 

 perpendicular to the 

 free surface. It would 

 be interesting, if it were 

 practicable, to learn 

 from experiment how 

 these prisms would be 

 further fractured by a 

 continuation of the com- 

 pression. From me- 

 chanical considerations involving the resolution of forces with refer- 

 ence to the ready-formed fractures, it seems probable that the next 

 series of fractures to form would bisect the angles of the first double 

 series or set. Wherever rocks are found exposed in their original 



55 



FIG. 36. A set of master joints developed in shale 

 upon the shores of Cayuga Lake near Ithaca, 

 New York (after U. S. G. S.). 



