brachiopods

• brachiopods

59:1.18The ma­rine life was much alike the world over and con­sisted of the sea­weeds, one-celled or­gan­isms, sim­ple sponges, trilo­bites, and other crus­taceans—shrimps, crabs, and lob­sters. Three thou­sand va­ri­eties of bra­chiopods ap­peared at the close of this pe­riod, only two hun­dred of which have sur­vived. These an­i­mals rep­re­sent a va­ri­ety of early life which has come down to the pres­ent time prac­ti­cally un­changed.

• brachiopods

59:2.12There were many va­ri­eties of shell an­i­mals, but their shells were not then so much needed for de­fen­sive pur­poses as in sub­se­quent ages. The gas­tropods were pres­ent in the wa­ters of the an­cient seas, and they in­cluded sin­gle-shelled drills, peri­win­kles, and snails. The bi­valve gas­tropods have come on down through the in­ter­ven­ing mil­lions of years much as they then ex­isted and em­brace the mus­sels, clams, oys­ters, and scal­lops. The valve-shelled or­gan­isms also evolved, and these bra­chiopods lived in those an­cient wa­ters much as they ex­ist to­day; they even had hinged, notched, and other sorts of pro­tec­tive ar­range­ments of their valves.

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.

59:3.2No fire rocks or lava are found in the stone lay­ers of this pe­riod ex­cept those of the great vol­ca­noes of south­ern Eu­rope and east­ern Maine and the lava flows of Que­bec. Vol­canic ac­tion was largely past. This was the height of great wa­ter de­po­si­tion; there was lit­tle or no moun­tain build­ing.

59:3.3290,000,000 years ago the sea had largely with­drawn from the con­ti­nents, and the bot­toms of the sur­round­ing oceans were sink­ing. The land masses were lit­tle changed un­til they were again sub­merged. The early moun­tain move­ments of all the con­ti­nents were be­gin­ning, and the great­est of these crustal up­heavals were the Hi­malayas of Asia and the great Cale­do­nian Moun­tains, ex­tend­ing from Ire­land through Scot­land and on to Spitzber­gen.

59:3.4It is in the de­posits of this age that much of the gas, oil, zinc, and lead are found, the gas and oil be­ing de­rived from the enor­mous col­lec­tions of veg­etable and an­i­mal mat­ter car­ried down at the time of the pre­vi­ous land sub­mer­gence, while the min­eral de­posits rep­re­sent the sed­i­men­ta­tion of slug­gish bod­ies of wa­ter. Many of the rock salt de­posits be­long to this pe­riod.

59:3.5The trilo­bites rapidly de­clined, and the cen­ter of the stage was oc­cu­pied by the larger mol­lusks, or ceph­a­lop­ods. These an­i­mals grew to be fif­teen feet long and one foot in di­am­e­ter and be­came mas­ters of the seas. This species of an­i­mal ap­peared sud­denly and as­sumed dom­i­nance of sea life.

59:3.6The great vol­canic ac­tiv­ity of this age was in the Eu­ro­pean sec­tor. Not in mil­lions upon mil­lions of years had such vi­o­lent and ex­ten­sive vol­canic erup­tions oc­curred as now took place around the Med­i­ter­ra­nean trough and es­pe­cially in the neigh­bor­hood of the British Isles. This lava flow over the British Isles re­gion to­day ap­pears as al­ter­nate lay­ers of lava and rock 25,000 feet thick. These rocks were laid down by the in­ter­mit­tent lava flows which spread out over a shal­low sea bed, thus in­ter­spers­ing the rock de­posits, and all of this was sub­se­quently el­e­vated high above the sea. Vi­o­lent earth­quakes took place in north­ern Eu­rope, no­tably in Scot­land.

59:3.7The oceanic cli­mate re­mained mild and uni­form, and the warm seas bathed the shores of the po­lar lands. Bra­chio­pod and other ma­rine-life fos­sils may be found in these de­posits right up to the North Pole. Gas­tropods, bra­chiopods, sponges, and reef-mak­ing corals con­tin­ued to in­crease.

59:3.8The close of this epoch wit­nesses the sec­ond ad­vance of the Sil­urian seas with an­other com­min­gling of the wa­ters of the south­ern and north­ern oceans. The ceph­a­lop­ods dom­i­nate ma­rine life, while as­so­ci­ated forms of life pro­gres­sively de­velop and dif­fer­en­ti­ate.

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.

59:3.10The cli­mate is even and mild, and ma­rine fos­sils are laid down in the arc­tic re­gions. But by the end of this epoch the seas are so ex­ces­sively salty that lit­tle life sur­vives.

59:3.11To­ward the close of the fi­nal Sil­urian sub­mer­gence there is a great in­crease in the echin­o­derms—the stone lilies—as is ev­i­denced by the crinoid lime­stone de­posits. The trilo­bites have nearly dis­ap­peared, and the mol­lusks con­tinue monar­chs of the seas; coral-reef for­ma­tion in­creases greatly. Dur­ing this age, in the more fa­vor­able lo­ca­tions the prim­i­tive wa­ter scor­pi­ons first evolve. Soon there­after, and sud­denly, the true scor­pi­ons—ac­tual air breathers—make their ap­pear­ance.

59:3.12These de­vel­op­ments ter­mi­nate the third ma­rine-life pe­riod, cov­er­ing twenty-five mil­lion years and known to your re­searchers as the Sil­urian.

• brachiopods

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.