44 



HAEHL AND ARNOLD — THE MIOCENE DIABASE. [Feb. 5, 



Other Minerals. — Magnetite and some ilmenite are present in the 

 diabase as grains and irregular masses. Grouping is occasionally 

 seen, but for the most part both of these minerals are scattered 

 through the mass without definite position. 



Apatite is sparingly present in its usual characteristic clear, long, 

 slender prisms, included by the other constituents. 



Of the secondary products analcite is by far the most important. 

 It occurs chiefly in the feldspars in the diabasic facies. In no in- 

 stance could it be shown that it is other than a secondary product, 

 nor does it indicate an origin other than of an alteration product 

 of the feldspars. Treated with hydrochloric acid it is soluble, but 

 forms no jelly. 



Fig. 22. Section of secondary dike. (A), analcite; (P), augite; (F), feld- 

 spar. X 30- 



The Secondary Dikes. — In thin sections the rocks of the second- 

 ary dikes contain apatite, magnetite, augite, sphene, feldspar, pyrite, 

 analcite and natrolites (see Fig. 22). The sections are particu- 

 larly clear and fresh. 



The feldspars are plagioclases with the composition of labrador- 

 ite. They are broadly lath-shaped and show Albite twinning. Wavy 

 extinction with a basic interior and more acid periphery is common 



