. Bulletin of the Geological Society of America. Geology. KHyjliMS IN DPJXIDATTON 771 the stage of old age, great areas oi' Paleozoic and Mesozoic sediments will iiave become destroyed. But nature reveals while she destroys, and be- ca;use of this very fact of the contrast of the [present to the past the com- prehensive study oT the stratigraphic record is made \ery much easier than it would have l)ecii in the a\'erage coiidition of the lands, and in this particular century has been further facilitated through the fresh ex- posures made hy man incidental to his development of transportation sy
. Bulletin of the Geological Society of America. Geology. KHyjliMS IN DPJXIDATTON 771 the stage of old age, great areas oi' Paleozoic and Mesozoic sediments will iiave become destroyed. But nature reveals while she destroys, and be- ca;use of this very fact of the contrast of the [present to the past the com- prehensive study oT the stratigraphic record is made \ery much easier than it would have l)ecii in the a\'erage coiidition of the lands, and in this particular century has been further facilitated through the fresh ex- posures made hy man incidental to his development of transportation systems. The existence of a mantle of sedimentary rocks, mostly marine, cover- ing three-(.|uai'tej-s of the land surfaces, proNcs that since tiie opening of. -3,000. -⢠Figure âHypsoyiaphiv Curee of the Continents and its Relation to the Paot A. Curve of continental relief, showing relations of altitude to area. R. Curve giving one-fourth relief, representative of periods of wide epeiric seas. 'â - Limicii of periodic oscillations of sealevel to flood two-thirds of continental area with profile B. the MidcUe Cambrian these have, on the whole receiyfid sedinn^nt rnther than, supplied it. Of course, there has been alternating deposition ,, IJiiknown amounts are gone, but the balance was in favor of accumulation of sediments. Marine shales, and limestones are the most \A"ide-spread of formations. Through most of geologic time .the continents have lain awash with the ocean level and across them the rising ocean floods have flowed. The sediment' of these Paleozoic anrl Mesozoic times came in o-reatest bulk from the limifp'd. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Geological Society of America. [New York : The Society]
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
