Devonian

59:4.1In the age­long strug­gle be­tween land and wa­ter, for long pe­ri­ods the sea has been com­par­a­tively vic­to­ri­ous, but times of land vic­tory are just ahead. And the con­ti­nen­tal drifts have not pro­ceeded so far but that, at times, prac­ti­cally all of the land of the world is con­nected by slen­der isth­muses and nar­row land bridges.

59:4.2As the land emerges from the last Sil­urian in­un­da­tion, an im­por­tant pe­riod in world de­vel­op­ment and life evo­lu­tion comes to an end. It is the dawn of a new age on earth. The naked and unattrac­tive land­scape of for­mer times is be­com­ing clothed with lux­u­ri­ant ver­dure, and the first mag­nif­i­cent forests will soon ap­pear.

59:4.3The ma­rine life of this age was very di­verse due to the early species seg­re­ga­tion, but later on there was free com­min­gling and as­so­ci­a­tion of all these dif­fer­ent types. The bra­chiopods early reached their cli­max, be­ing suc­ceeded by the arthro­pods, and bar­na­cles made their first ap­pear­ance. But the great­est event of all was the sud­den ap­pear­ance of the fish fam­ily. This be­came the age of fishes, that pe­riod of the world’s his­tory char­ac­ter­ized by the ver­te­brate type of an­i­mal.

59:4.4270,000,000 years ago the con­ti­nents were all above wa­ter. In mil­lions upon mil­lions of years not so much land had been above wa­ter at one time; it was one of the great­est land-emer­gence epochs in all world his­tory.

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.

59:4.6260,000,000 years ago, to­ward the end of this land-de­pres­sion epoch, North Amer­ica was par­tially over­spread by seas hav­ing si­mul­ta­ne­ous con­nec­tion with the Pa­cific, At­lantic, Arc­tic, and Gulf wa­ters. The de­posits of these later stages of the first De­vo­nian flood av­er­age about one thou­sand feet in thick­ness. The coral reefs char­ac­ter­iz­ing these times in­di­cate that the in­land seas were clear and shal­low. Such coral de­posits are ex­posed in the banks of the Ohio River near Louisville, Ken­tucky, and are about one hun­dred feet thick, em­brac­ing more than two hun­dred va­ri­eties. These coral for­ma­tions ex­tend through Canada and north­ern Eu­rope to the arc­tic re­gions.

59:4.7Fol­low­ing these sub­mer­gences, many of the shore lines were con­sid­er­ably el­e­vated so that the ear­lier de­posits were cov­ered by mud or shale. There is also a red sand­stone stra­tum which char­ac­ter­izes one of the De­vo­nian sed­i­men­ta­tions, and this red layer ex­tends over much of the earth’s sur­face, be­ing found in North and South Amer­ica, Eu­rope, Rus­sia, China, Africa, and Aus­tralia. Such red de­posits are sug­ges­tive of arid or semi­arid con­di­tions, but the cli­mate of this epoch was still mild and even.

59:4.8Through­out all of this pe­riod the land south­east of the Cincin­nati Is­land re­mained well above wa­ter. But very much of west­ern Eu­rope, in­clud­ing the British Isles, was sub­merged. In Wales, Ger­many, and other places in Eu­rope the De­vo­nian rocks are 20,000 feet thick.

59:4.9250,000,000 years ago wit­nessed the ap­pear­ance of the fish fam­ily, the ver­te­brates, one of the most im­por­tant steps in all pre­hu­man evo­lu­tion.

59:4.10The arthro­pods, or crus­taceans, were the an­ces­tors of the first ver­te­brates. The fore­run­ners of the fish fam­ily were two mod­i­fied arthro­pod an­ces­tors; one had a long body con­nect­ing a head and tail, while the other was a back­bone­less, jaw­less pre­fish. But these pre­lim­i­nary types were quickly de­stroyed when the fishes, the first ver­te­brates of the an­i­mal world, made their sud­den ap­pear­ance from the north.

59:4.11Many of the largest true fish be­long to this age, some of the teeth-bear­ing va­ri­eties be­ing twenty-five to thirty feet long; the pres­ent-day sharks are the sur­vivors of these an­cient fishes. The lung and ar­mored fishes reached their evo­lu­tion­ary apex, and be­fore this epoch had ended, fishes had adapted to both fresh and salt wa­ters.

59:4.12Ver­i­ta­ble bone beds of fish teeth and skele­tons may be found in the de­posits laid down to­ward the close of this pe­riod, and rich fos­sil beds are sit­u­ated along the coast of Cal­i­for­nia since many shel­tered bays of the Pa­cific Ocean ex­tended into the land of that re­gion.

59:4.13The earth was be­ing rapidly over­run by the new or­ders of land veg­e­ta­tion. Here­to­fore few plants grew on land ex­cept about the wa­ter’s edge. Now, and sud­denly, the pro­lific fern fam­ily ap­peared and quickly spread over the face of the rapidly ris­ing land in all parts of the world. Tree types, two feet thick and forty feet high, soon de­vel­oped; later on, leaves evolved, but these early va­ri­eties had only rudi­men­tary fo­liage. There were many smaller plants, but their fos­sils are not found since they were usu­ally de­stroyed by the still ear­lier ap­pear­ing bac­te­ria.

59:4.14As the land rose, North Amer­ica be­came con­nected with Eu­rope by land bridges ex­tend­ing to Green­land. And to­day Green­land holds the re­mains of these early land plants be­neath its man­tle of ice.

59:4.15240,000,000 years ago the land over parts of both Eu­rope and North and South Amer­ica be­gan to sink. This sub­si­dence marked the ap­pear­ance of the last and least ex­ten­sive of the De­vo­nian floods. The arc­tic seas again moved south­ward over much of North Amer­ica, the At­lantic in­un­dated a large part of Eu­rope and west­ern Asia, while the south­ern Pa­cific cov­ered most of In­dia. This in­un­da­tion was slow in ap­pear­ing and equally slow in re­treat­ing. The Catskill Moun­tains along the west bank of the Hud­son River are one of the largest ge­o­logic mon­u­ments of this epoch to be found on the sur­face of North Amer­ica.

59:4.16230,000,000 years ago the seas were con­tin­u­ing their re­treat. Much of North Amer­ica was above wa­ter, and great vol­canic ac­tiv­ity oc­curred in the St. Lawrence re­gion. Mount Royal, at Mon­treal, is the eroded neck of one of these vol­ca­noes. The de­posits of this en­tire epoch are well shown in the Ap­palachian Moun­tains of North Amer­ica where the Susque­hanna River has cut a val­ley ex­pos­ing these suc­ces­sive lay­ers, which at­tained a thick­ness of over 13,000 feet.

59:4.17The el­e­va­tion of the con­ti­nents pro­ceeded, and the at­mo­sphere was be­com­ing en­riched with oxy­gen. The earth was over­spread by vast forests of ferns one hun­dred feet high and by the pe­cu­liar trees of those days, silent forests; not a sound was heard, not even the rus­tle of a leaf, for such trees had no leaves.

59:4.18And thus drew to a close one of the longest pe­ri­ods of ma­rine-life evo­lu­tion, the age of fishes. This pe­riod of the world’s his­tory lasted al­most fifty mil­lion years; it has be­come known to your re­searchers as the De­vo­nian.