170 



Subsurface Geologic Methods 



The study of sedimentary rocks by petrofabric methods has been 

 comparatively neglected. Ingerson ^~ indicates that valuable information 

 on current direction may be gained from the fabric study of sediments. 



Figure 67. Pronounced lineation parallel to b axis of fold. The angle this lineation 

 makes with the horizontal gives the plunge of the fold. The joints normal to the 

 lineation are a-c joints. 



Wayland ^^ has shown that tlie tendency of the long axis of quartz 

 grains is to be parallel to the c axis and that the c axis lies nearly parallel 

 to the bedding plane in sandstones. 



Size and shape of fragmental materials in clastic sedimentary rocks 



^- Ingerson, Earl, Fabric Criteria for Distinguishing Pseudo-Ripple Marks from Ripple Marks: Geol. 

 Soc. America Bull., vol. 51, pp. 557-570, 1940. 



^ Wayland, R. G., Optical Orientation in Elongate Clastic Quartz: Amer. Jour. Sci., vol. 237, pp. 

 99-109, 1939. 



