BULL. GEOL. SOC. AM. 



VOL. 18, 1905. PL. 71 



BLUFF BACK OF DELAWARE MINE 



Taken by W. .T. I'enliallegon. August. 1007, to illustrate 

 effect ol' wentluu-iuK on (iphitic texture. The wliite ob.iect 

 Ls a slide rule six inches long and one ineli wide. The ex- 

 posure is about l(tl) feet from the base of the "gi'eeu- 

 stone" 



i 



