quartz

60:3.3This pe­riod thus be­comes the mod­ern moun­tain-build­ing stage of ge­o­logic his­tory. Prior to this time there were few moun­tain peaks, merely el­e­vated land ridges of great width. Now the Pa­cific coast range was be­gin­ning to el­e­vate, but it was lo­cated seven hun­dred miles west of the pres­ent shore line. The Sier­ras were be­gin­ning to form, their gold-bear­ing quartz strata be­ing the prod­uct of lava flows of this epoch. In the east­ern part of North Amer­ica, At­lantic sea pres­sure was also work­ing to cause land el­e­va­tion.

59:1.16The trilo­bite fos­sil-bear­ing strata of this epoch out­crop here and there through­out all the con­ti­nents ex­cept in cen­tral Asia. In many re­gions these rocks are hor­i­zon­tal, but in the moun­tains they are tilted and dis­torted be­cause of pres­sure and fold­ing. And such pres­sure has, in many places, changed the orig­i­nal char­ac­ter of these de­posits. Sand­stone has been turned into quartz, shale has been changed to slate, while lime­stone has been con­verted into mar­ble.

59:3.1300,000,000 years ago an­other great pe­riod of land sub­mer­gence be­gan. The south­ward and north­ward en­croach­ment of the an­cient Sil­urian seas made ready to en­gulf most of Eu­rope and North Amer­ica. The land was not el­e­vated far above the sea so that not much de­po­si­tion oc­curred about the shore lines. The seas teemed with lime-shelled life, and the falling of these shells to the sea bot­tom grad­u­ally built up very thick lay­ers of lime­stone. This is the first wide­spread lime­stone de­posit, and it cov­ers prac­ti­cally all of Eu­rope and North Amer­ica but only ap­pears at the earth’s sur­face in a few places. The thick­ness of this an­cient rock layer av­er­ages about one thou­sand feet, but many of these de­posits have since been greatly de­formed by tilt­ing, up­heavals, and fault­ing, and many have been changed to quartz, shale, and mar­ble.