1904.] HAEHL AND ARNOLD— THE MIOCENE DIABASE. 45 



Kaolinization is somewhat advanced; dust-like inclusions, together 

 with augite and magnetite, are frequent. 



The augites are of the pale purplish-brown variety with slight ple- 

 ochroism. They make up an unusually small percentage of the 

 rock, however. Basal sections show wavy extinction. Both idio- 

 morphic and allotriomorphic cr3^stals are present. Cleavage is 

 distinct and relief high. Inclusions of feldspar and magnetite are 

 numerous and decomposition very slight. 



Magnetite is present in unusual quantities and in very striking, 

 long, slender rods, as well as in its common tabular forms. A few 

 crystals of pyrite were noted, also a wedge-shaped crystal of sphene. 



Analcite and natrolite are present in these sections in greater 

 quantity than in those of any other portion of the mass. 



Fig. 23. Section of the basaltic facies (specimen 38), showing basaltic and flow 

 structure. (O), olivine; (0')i olivine weathering to iddingsite ; (F), feld- 

 spar crystal with etched edges ; (A), augite. x 20. Photograph by Ralph 

 Arnold. 



The Basaltic Facies. 



In thin section the basaltic facies of the igneous mass presents a 

 more difficult problem than the diabasic type, because it is univer- 

 sally more weathered. The typical section shows a fev/ phenocrysts 

 of olivine and augite in a fine-grained ground mass of lath-shaped 

 feldspars, microscopic augites and olivines, ilmenite, magnetite, 

 and the secondary products — calcite, serpentine, chlorite, iddings- 

 ite, iron oxides, natrolite and analcite. 



