Morgan and Tallmon — Occurrence of Bitumen. 377 



origin, neither should the association of bitumen with boric acid 

 be considered as a strong indication of volcanic origin for the 

 bitumen. 



University of California, Berkeley, California. 



EXPLANATION OF PLATE XVIII. 



Figure 1. — Side view of egg. 



Figure 2. — Egg in the original matrix. 



Figure 3. — Matrix from inner side, showing pits. 



Figure 4. — In the matrix, end view. 



(All figures natural size. ) 



Measurements. 



Length of egg 62 mm 



Width " " 40 



Circumference (longitudinally) 169 



" (transversely) 124 



Long diameter of enclosing capsule 120 



Average thickness of enclosing capsule 12 



Thickness of eggshell "33 



EXPLANATION OF PLATE XIX. 



Figure 1. — Fractured surface of the broken egg, showing the contents ; t, t' , 

 and other darkened areas represent the bituminous material ; the remainder 

 of the cavity is filled with colemanite. (Natural size.) 



Figure 2a. ~ A portion of the eggshell ground down on one side, s, corru- 

 gated outer surface : c, cellular lower layer. ( x 275.) 



Figure 2b. — Cross-section of the shell fragment shown in figure 2a. s, 

 corrugated outer surface ; c, cellular lower layer. ( x 275.) 



Figure 3. — Outer surface of the shell, showing corrugations of the surface 

 and a large pit filled with bituminous material. ( x 275.) 



Figure 4. — Cross-section of the pit shown in figure 3. ( x 275.) 



