38 EARTH FEATURES AND THEIR MEANING 



Later, when cemented together, these become in order, coarser 

 and finer sandstones, shales, and limestones. The order of super- 

 position, reading from the bottom to the top, thus gives the order 

 of decreasing age of the formations. 



A subsequent uplift of the coast will be accompanied by a 

 recession of the sea, and when later dissected by nature for our 

 inspection, the order of superposition and the individual character 

 of each of the deposits may be studied at leisure. From such 

 studies it has been found that along with the inorganic deposits 

 there are often found the remains of life in the hard parts of such 

 invertebrate animals as the mollusks and the Crustacea. These 

 so-called fossils represent animals which were gradually developed 

 from simpler to more and more complex forms; and they thus 

 serve the purpose of successive page numbers in arranging the 

 order of disturbed strata, at the same time that they supply 

 the most secure foundation upon which rests the great doctrine 

 of evolution. 



The basins of earlier ages. It was the great Viennese geolo- 

 gist, Professor Suess, who first pointed out that in mountain regions 

 there are found the thickest and the most complete series of the 

 marine deposits; whereas outside these provinces the forma- 

 tions are separated by wide gaps representing periods when no 

 deposits were laid down because the sea had retired from the 

 region. The completeness of the series of deposits in the mountain 

 districts can only be interpreted to mean that where these but 

 lately formed mountains rise to-day, were for long preceding ages 

 the basins for deposition of terrigenous sediments. It would 

 seem that the lithosphere in its adjustment had selected these 

 earlier sea basins with their heavy layers of sediment for zones of 

 special uplift. 



The deposits of the deep sea. Outside the continental slope, 

 whose base marks the limit of the terrigenous deposits, lies the 

 deeper sea, for the most part a series of broad plains, but varied by 

 more profound steep-walled basins, the so-called " deeps " of the 

 ocean. As shown by the dredgings of the Challenger expedi- 

 tion and others of more recent date, the deposits upon the ocean 

 floor are of a wholly different character from those which are 

 derived from the continents. Except in the great deeps, or 

 between depths of five hundred and fifteen hundred fathoms, 



