340 Proceedings of the Royal Physical Society. 



may probably be discovered. But on the British coasts 

 instances of such terraces seem to be very rare. The author 

 of these remarks was at one time led to suppose that hori- 

 zontal surfaces might as frequently be produced under 

 water as above it. On further investigation, however, he 

 sees that he was mistaken. The soundings given in the 

 charts do not indicate in any place a regular level terrace 

 below low-water mark ; and he would refer to the experience 

 and observation of the members of the Koyal Physical 

 Society whether they can point out any instances of level 

 terraces formed under the water in places that are affected 

 by the tide. The inquiry possesses considerable interest for 

 those who engage in geological speculations. If, on full 

 examination, it shall be found that, while level terraces above 

 high- water mark are in constant process of formation, there 

 are very few, if any, now forming under low-water mark, 

 we are naturally led to conclude that the ancient sea-mar- 

 gins found along our coasts were not deposited, as some 

 seem to imagine, at the bottom of the sea, but were thrown 

 up on the shore, in the same manner as those that we now 

 see forming there. As a further proof that the terrace or level 

 platform which we so frequently find on the sea-shore, some 

 10 or 15 feet above ordinary high- water mark, has been 

 thrown up by the advancing billow, and has not been formed, 

 as some suppose, beneath the water, we may refer to the 

 fact, that the shells found in these terraces do not lie in the 

 position which they must have occupied in their native bed, 

 but are heaped together in a confused mass ; while no limpet 

 or shell of similar nature is found adhering to the rocks that 

 rise above the level of the terrace. 



Height of Terrace in Relation to the Ordinary Level 

 of the Sea. 



"When the terrace is formed by the advancing wave, its 

 elevation above ordinary flood-mark must depend on the 

 force with which the billow is driven against the beach. 

 On those parts of the western coast of Scotland, for instance, 

 which are exposed to the full swell of the Atlantic, they 

 will rise much higher than on our eastern snores, and any 



