shale

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.

59:5.15The coal lay­ers al­ter­nate with shale, stone, and con­glom­er­ate. These coal beds over cen­tral and east­ern United States vary in thick­ness from forty to fifty feet. But many of these de­posits were washed away dur­ing sub­se­quent land el­e­va­tions. In some parts of North Amer­ica and Eu­rope the coal-bear­ing strata are 18,000 feet in thick­ness.

59:1.123. Shales—de­posits made in the deeper and more quiet wa­ter.

59:5.10The de­posits of this early Car­bonif­er­ous age are from 500 to 2,000 feet thick, con­sist­ing of sand­stone, shale, and lime­stone. The old­est strata yield the fos­sils of both land and ma­rine an­i­mals and plants, along with much gravel and basin sed­i­ments. Lit­tle work­able coal is found in these older strata. These de­po­si­tions through­out Eu­rope are very sim­i­lar to those laid down over North Amer­ica.

60:1.1The ero­sion de­posits of this pe­riod were mostly con­glom­er­ates, shale, and sand­stone. The gyp­sum and red lay­ers through­out these sed­i­men­ta­tions over both Amer­ica and Eu­rope in­di­cate that the cli­mate of these con­ti­nents was arid. These arid dis­tricts were sub­jected to great ero­sion from the vi­o­lent and pe­ri­odic cloud­bursts on the sur­round­ing high­lands.

60:3.9The de­posits of chalk and green­sand marl give name to this pe­riod. The sed­i­men­ta­tions of these times are var­ie­gated, con­sist­ing of chalk, shale, sand­stone, and small amounts of lime­stone, to­gether with in­fe­rior coal or lig­nite, and in many re­gions they con­tain oil. These lay­ers vary in thick­ness from 200 feet in some places to 10,000 feet in west­ern North Amer­ica and nu­mer­ous Eu­ro­pean lo­cal­i­ties. Along the east­ern bor­ders of the Rocky Moun­tains these de­posits may be ob­served in the up­tilted foothills.

58:7.10Some of the up­per lay­ers of these tran­si­tion rock de­posits con­tain small amounts of shale or slate of dark col­ors, in­di­cat­ing the pres­ence of or­ganic car­bon and tes­ti­fy­ing to the ex­is­tence of the an­ces­tors of those forms of plant life which over­ran the earth dur­ing the suc­ceed­ing Car­bonif­er­ous or coal age. Much of the cop­per in these rock lay­ers re­sults from wa­ter de­po­si­tion. Some is found in the cracks of the older rocks and is the con­cen­trate of the slug­gish swamp wa­ter of some an­cient shel­tered shore line. The iron mines of North Amer­ica and Eu­rope are lo­cated in de­posits and ex­tru­sions ly­ing partly in the older un­strat­i­fied rocks and partly in these later strat­i­fied rocks of the tran­si­tion pe­ri­ods of life for­ma­tion.

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.