1917] Eaklc: Minerals Associated ivith Crystalline Limestone 329 



visits. The cement contains the calcined remains of many beautiful, 

 rare, and perhaps new, mineral species. 



Hills and Quarries. — The Crestmore limestone forms two hills 

 closely connected by a saddle-ridge. Both hills rest upon a common 

 base of granodiorite somewhat elliptical in contour, with its longer axis 

 trending northeast-southwest. The north is called Sky Blue Hill 

 because of its blue calcite ; while the south hill, having pure white 

 marble, has been designated Chino Hill. Sky Blue Hill has a large 

 quarry on its northern side called North Star quarry, a larger one on 

 its eastern side named the Commercial Rock quarry, and between them 

 a third one, the Lone Star quarry, has recently been opened. Chino 

 Hill has one large quarry on its southwest side, and the accompanying 

 view (pi. 21) shows this quarry and the plant of the cement company. 

 The floor of the quarry marks approximately the juncture of the 

 igneous base with the limestone capping. 



The limestone forming the capping is a small remnant of a more 

 extensive body of limestone which formerly covered this region. There 

 is a larger mass similar to Crestmore about three miles west, and Slover 

 Mountain near Colton may be another remnant left as a capping upon 

 an intrusive mass. 



Intrusive Rocks. — There are three types of igneous intrusives occur- 

 ring in the hills and all three have been active agents in the meta- 

 morphism of the limestone. Granodiorite, quartz-monzonite porphyry 

 and pegmatite are present and intimately associated with the contact 

 phenomena. 



The granodiorite is a hornblende-biotite rock with a fairly coarse 

 granitic structure consisting essentially of orthoclase, plagioclase, 

 hornblende, biotite, and quartz. The orthoclase, which appears to 

 constitute the main portion of the rock, is mostly white, and the rock 

 is consequently gray as the prevailing color, but patches of brick-red 

 orthoclase occur, giving the rock a red color. Labradorite and oligo- 

 clase are the triclinic feldspars present, but very little albite twinning 

 is seen. The rock is not fresh and all of the feldspars are muddy and 

 opaque. The dark silicates are mostly black hornblende, which is 

 dark green in thin section, and a few plates of biotite. Quartz is much 

 subordinate to the feldspars in amount. 



This granodiorite is used by the company as a substitute for clay 

 in the cement. Daily analyses of it are made and three of them will 

 serve to show the relative proportions of the bases. 



