STRATIFIED ROCKS. 181 



The clay-rocks, in their incoherent condition, are beds 

 of clay, brick-earth, mud, and ooze. In their coherent 

 condition they are the same cemented into shales, or, still 

 harder, into slates. 



Lime-rocks, in an incoherent condition, are lime-muds, 

 such as exist now in coral lagoons, or in the deep sea (glo- 

 bigerina ooze, page 117) ; in a slightly consolidated con- 

 dition they are chalks, and in a stony condition they are 

 limestones, marbles, and travertines. 



These different kinds may each produce varieties oi 

 different color and grain. They also pass by mixture 

 insensibly into each other, and thus form infinite varie- 

 ties. Thus we may have an argillaceous or calcareous 

 sandstone or calcareous shale, etc. 



All that need further be said on the subject of the 

 origin of stratified rocks is best thrown into a series oi 

 propositions, very simple and yet underlying all geologi- 

 cal reasonings : 



1. Stratified Rocks are more or less Consolidated 

 Sediments. This has been thus far assumed. We wish 

 now to direct the pupil to the observation of the evidence : 

 a. Every gradation may be traced between muds, clays, 

 and sands, which we know were deposited in water ; and 

 shales and sandstones, which we find forming the strata 

 of mountains, ft. In many cases we may see the process 

 of hardening going on under our eyes. For example, at 

 the mouths of rivers carrying lime in solution, like the 

 Rhine, the river-silts are consolidated into calcareous 

 shales. On the shores of coral reefs we find coral mud, 

 coral sand, and coral breccia consolidated into peculiar 

 limestones (page 108). c. Close examination of many 

 rocks, especially sandstones and shales, clearly shows the 

 sorting of material (water-sorting) along the lines of lam- 

 ination, d. As shells and skeletons of animals are now 

 imbedded in muds of rivers, lakes, and seas, so fossils are 

 found in stratified rocks, e. Other marks, which occur 



