GEOIvOGY or' IvA SALINE COUNTY. 



9 



then must have had a slope- or inclination equal to that 

 of the shore on which they were deposited, and were, 

 probably, thinnest on the shore side, in the case of nar- 

 row seas, the thickest beds being- probably in the mid- 

 dle, or, at least, at a distance from the shore, or in the 

 nei^rhborhood of the mouths of g-reat rivers, just as 

 todav vast masses of material are being- piled up near 

 the mouths of the Mississippi and other g-reat streams. 



On an ocean beach, exposed to the full sweep of 

 the waves, we find few perfect shells, the constant 

 movement of the restless waters keeping- them in 

 motion, and in a short time reducing- even thick and 

 heavy ones to frag'ments, so that it is only in sheltered 

 nooks, under the lee of islands, or in well protected 

 bays, that \> e may hope to find the strand strewn with 

 the treasures of the deep. But more than this, shell 

 fish usually live in colonies as the oyster, mussel and 

 clam, or in places where they can most easily procure 

 their food, and althoug-h to anything- that can swim the 

 whole realm of ocean seems open, yet we find even fast 

 swimming- fishes restricted to certain parts of the sea, 

 and their bounds as fixed and changfeless as the g-reat 

 mountain chains which form the barriers between 

 nations. Thus ocean currents, the temperature of the 

 water, the material for food, all these are factors in 

 the distribution of marine life. Then some creatures 

 cannot endure mud-laden water; others flourish in it; 

 some fatten on decaying- veg-etation, some shun it as if 

 it were destruction to them, so that the remains that 

 may be entombed in the deposits of a coast will depend 

 upon many elements of which we may be able to ascer- 

 tain but two or three, but we may rest assured that 

 extensive deposits of shells and other org-anic remains 

 are certain indices of quiet waters except in the case of 

 coral reefs and an abundant, regular supply of food, 



