26 Nezv York State Museum 



mountain, building up through their continued action ex- 

 tensive deposits of sand and clay of great thickness which 

 are known as piedmont deposits (Latin pes, foot; mons, 

 mountain). Deltas deposited by rivers whether in lake 

 or sea are regarded as so much reclaimed land and belong 

 with continental deposits. They have a characteristic 

 structure which will be taken up later under structures 

 of rocks. Fossils of delta formations will be terrestrial 

 if the formations were laid down in a lake, and an inter- 

 mingling of land and sea life if the delta was deposited 

 in the sea. Always, the presence of land life only in 

 formations indicates continental deposition. Glacial 

 and fluvio-glacial deposits also belong with continental 

 deposits. 



Littoral deposits are the beach or strand deposits laid 

 down between the tidal limits. The area covered by such 

 deposits varies in extent depending upon the tidal range 

 and the slope of the land. Where the slope of the land 

 is very gradual there are tidal lagoons, salt marshes and 

 shallow sounds and estuaries where mud flats are exposed 

 at low tide. Here sands and muds are deposited. In 

 general along the beach the area exposed by the tides is 

 relatively narrow, and besides is so exposed to the action 

 of the waves and tidal currents that the finer materials 

 are washed away and only the coarser sands and gravels 

 accumulate. Such deposits form conglomerates and 

 coarse sandstone rocks but they are never very thick. 

 Where land is building out to sea they are buried under 

 land deposits, and when the sea encroaches upon the land 

 they are buried under marine deposits. 



Marine deposits are those laid down beyond the limit 

 of low tide. The most active deposition goes on in the 

 shallow sea or flachsee which covers the continental shelf 



