21 S Dana and Chambers on Ancient Sea-Margins. 



neglected by Mr Chambers and many others in the study of 

 terraces. It is this : That the marine origin of a bed is to 

 be proved by its resemblance to marine formations, and its 

 containing marine relics. Consider for a moment the cha- 

 racters of a line of coast. 



1. In many places above the water-line, there are beach- 

 accumulations ; and these accumulations are sandy, and dis- 

 tinctly stratified. The layers, though thin and distinct, are 

 irregular ; not of very great lateral extent, but frequently 

 blending and changing their direction. There is often a 

 slope in the layers, having the inclination of a beach. 



2. There are drift-heaps on many exposed coasts, formed 

 by the vi^ind and higher seas, above the true beach-accumu- 

 lations. These also are stratified (or laminated w^hen soli- 

 dified), each sheet of sand blown over forming a separate 

 layer. The layers are very irregular in dip, often curving 

 (like the top of the drift-heap), and frequently changing their 

 direction. They are often cut off abruptly, and overlaid un- 

 conformably by other layers, as a sand-drift is often beheaded 

 by a gale, again to increase by new accumulations. Such 

 drift-heaps sometimes form interrupted ridges along a coast, 

 40, 50, or 60 feet in height. 



3. Below the water level, there are often flats or slopes of 

 gravel, sand, or silt. The material is frequently in delicate 

 layers, and the layers may be of wide or small extent, often 

 (when in extended banks) scarcely varying from horizon- 

 tality, yet sloping where the bottom slopes. They are fre- 

 quently rippled by the waves, or agitated into parallel ridges, 

 in some cases even at a depth of 500 feet, and flexures like 

 those of the rippled surface will be apparent in the layers be- 

 neath. Again, when the waves on a shore break and flow 

 over a bank in shallow waters, they roll up the sand in a 

 series of slopes : such banks may, therefore, be composed of 

 horizontal layers, while the layers themselves occasionally 

 consist of subordinate inclined layers. 



4. The sandy beaches, in some places, contain worn shells; 

 but very frequently they are destitute of such remains, owing 

 to the trituration of the sands destroying those that may be 



