limestone

• limestone

59:4.5Five mil­lion years later the land ar­eas of North and South Amer­ica, Eu­rope, Africa, north­ern Asia, and Aus­tralia were briefly in­un­dated, in North Amer­ica the sub­mer­gence at one time or an­other be­ing al­most com­plete; and the re­sult­ing lime­stone lay­ers run from 500 to 5,000 feet in thick­ness. These var­i­ous De­vo­nian seas ex­tended first in one di­rec­tion and then in an­other so that the im­mense arc­tic North Amer­i­can in­land sea found an out­let to the Pa­cific Ocean through north­ern Cal­i­for­nia.

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.

59:1.134. Lime­stone—in­clud­ing the de­posits of trilo­bite shells in deep wa­ter.

59:2.3340,000,000 years ago there oc­curred an­other ex­ten­sive land sink­ing ex­cept in Asia and Aus­tralia. The wa­ters of the world’s oceans were gen­er­ally com­min­gled. This was a great lime­stone age, much of its stone be­ing laid down by lime-se­cret­ing al­gae.

59:3.9280,000,000 years ago the con­ti­nents had largely emerged from the sec­ond Sil­urian in­un­da­tion. The rock de­posits of this sub­mer­gence are known in North Amer­ica as Ni­a­gara lime­stone be­cause this is the stra­tum of rock over which Ni­a­gara Falls now flows. This layer of rock ex­tends from the east­ern moun­tains to the Mis­sis­sippi val­ley re­gion but not far­ther west ex­cept to the south. Sev­eral lay­ers ex­tend over Canada, por­tions of South Amer­ica, Aus­tralia, and most of Eu­rope, the av­er­age thick­ness of this Ni­a­gara se­ries be­ing about six hun­dred feet. Im­me­di­ately over­ly­ing the Ni­a­gara de­posit, in many re­gions may be found a col­lec­tion of con­glom­er­ate, shale, and rock salt. This is the ac­cu­mu­la­tion of sec­ondary sub­si­dences. This salt set­tled in great la­goons which were al­ter­nately opened up to the sea and then cut off so that evap­o­ra­tion oc­curred with de­po­si­tion of salt along with other mat­ter held in so­lu­tion. In some re­gions these rock salt beds are sev­enty feet thick.

59:5.8Two groups of echin­o­derms be­came es­pe­cially well de­vel­oped, and they are in re­al­ity the guide fos­sils of this epoch. The large shell-feed­ing sharks were also highly evolved, and for more than five mil­lion years they dom­i­nated the oceans. The cli­mate was still mild and equable; the ma­rine life was lit­tle changed. Fresh-wa­ter fish were de­vel­op­ing and the trilo­bites were near­ing ex­tinc­tion. Corals were scarce, and much of the lime­stone was be­ing made by the crinoids. The finer build­ing lime­stones were laid down dur­ing this epoch.

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.

60:1.4Over Eu­rope, es­pe­cially Ger­many and Rus­sia, may be found de­posits of this pe­riod. In Eng­land the New Red Sand­stone be­longs to this epoch. Lime­stone was laid down in the south­ern Alps as the re­sult of a sea in­va­sion and may now be seen as the pe­cu­liar dolomite lime­stone walls, peaks, and pil­lars of those re­gions. This layer is to be found all over Africa and Aus­tralia. The Car­rara mar­ble comes from such mod­i­fied lime­stone. Noth­ing of this pe­riod will be found in the south­ern re­gions of South Amer­ica as that part of the con­ti­nent re­mained down and hence pre­sents only a wa­ter or ma­rine de­posit con­tin­u­ous with the pre­ced­ing and suc­ceed­ing epochs.

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.

61:1.13Con­sid­er­able foraminiferal lime­stone was de­posited in Eu­ro­pean wa­ters. To­day this same stone is el­e­vated to a height of 10,000 feet in the Alps, 16,000 feet in the Hi­malayas, and 20,000 feet in Ti­bet. The chalk de­posits of this pe­riod are found along the coasts of Africa and Aus­tralia, on the west coast of South Amer­ica, and about the West In­dies.

57:8.13Through­out the oceanic ages, enor­mous lay­ers of fos­sil-free strat­i­fied stone were de­posited on this an­cient ocean bot­tom. (Lime­stone can form as a re­sult of chem­i­cal pre­cip­i­ta­tion; not all of the older lime­stone was pro­duced by ma­rine-life de­po­si­tion.) In none of these an­cient rock for­ma­tions will there be found ev­i­dences of life; they con­tain no fos­sils un­less, by some chance, later de­posits of the wa­ter ages have be­come mixed with these older pre­life lay­ers.