Identifier: evolutionofearth00barr (find matches)
Title: The evolution of the earth and its inhabitants; a series delivered before the Yale chapter of the Sigma xi during the academic year 1916-1917
Year: 1918 (1910s)
Authors: Barrell, Joseph, b. 1869 Schuchert, Charles, 1858-1942 Woodruff, Lorande Loss, 1879-1947 Lull, Richard Swann, 1867- Huntington, Ellsworth, 1876-1947
Subjects: Evolution Climatology Human beings -- Influence on nature Earth
Publisher: New Haven, Yale university press (etc., etc.)
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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sthat close the eras. Because the lands are then high they aresubject to more active erosion and in the last analysis all ofthe broken-up detrital and dissolved material is carried awayby the streams to the oceans. At these times the continents arealso largest and the materials received by the oceans are laiddown on the outermost edges of the lands, where subsequenttransgressions by the sea cover and hide them from ourobservation. After a long time the sea again comes to pressfurther and further upon the land and spreads more forma-tions of stratified rocks over those left by the previous flood-ings, the older geologic formations (see Fig. n). Thereforethere is upon the present continents between each two suchsuccessive formations a break in deposition, a hiatus in thegeologic record, a time interval when no record other thanerosion is at hand. These breaks in sedimentation arerepresentative of loss of record and are called intervals;they are regarded as the closing times of the eras.
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biJO 3 V O o O .0 t; V J3 u u CO I o s „• 4, g 5 co S ^ 2 >> _c a. 13S T3 s o AND ITS INHABITANTS 73 During these intervals when the continents are highest andlargest, the oceans are smallest in areal extent, the separatecontinents are often united by land-bridges as Panama unitesthe Americas, such bridges alter the direction of the greatocean streams like the Gulf Stream, the high mountain rangesalter the directions of the air currents and take out of themtheir moisture so that great desert areas arise like our inter-Rocky Mountain country, and because of these vast changesnearly all of the major movements are accompanied by glacialclimates. Such mighty changes in the geography, topography,and climate of the earth react strikingly upon the life of thepolar and temperate belts and so disarrange it that the majorintervals following the revolutions are spoken of as thecritical times in the earths history—critical not only for thegeography, separating or uniting continental m

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