PHYSICAL HISTORY AND GEOLOGY. 41 



some 50 or 60 feet would lay dry practically the whole archi- 

 pelago, as far as the great northern reef That such a condi- 

 tion of elevation at one time existed is, I believe, all but de- 

 monstrable ; and if this is true the present condition can only 

 be accounted for on one or two hypotheses : simple erosion or 

 erosion in combination with subsidence. The vast amount of 

 erosion that has taken place has already been referred to, and 

 it is barely necessary to enter further into its details. It will 

 immediately suggest itself to the inquiring mind that tliis ero- 

 sion could not well have taken place without subsidence, other- 

 wise it would be difficult to conceive, except under a condition 

 of very rapid elevation, how material could have initially ac- 

 cumulated, so as tolend itself to . destruction afterward. To 

 assume rapid elevation, followed by a period of stability when 

 destruction would exceed construction, requires the formula- 

 tion of cauFes which are not less difficult to receive than those 

 which would explain subsidence. Unquestionable evidences of 

 subsidence are, however, by no means wanting, and coincident- 

 ally they point to an amount of movement which would account 

 approximately for the depth of the great lagoon. Thus, in the 

 excavations made on Ireland Island for the lodgement of the 

 great floating dock, a deposit of peat,* and vegetable soil contain- 

 ing stumps of cedar in a vertical position, together with other 

 vegetable remains, and shells of the common sub-fossil land- 

 snail of the islands, were found at a depth beneath the water 

 of some 45 to 50 feet. The depth of the peat-bog which occu- 

 pies the central part of Main Island, has already been noticed. 

 It seems to be a not uncommon occurrence, as we were in- 

 formed by the keeper of the light at St. David's, that stumps 

 and roots of cedars are drawn up by the anchor chains of ves- 

 sels riding in the waters about St. George's. 



The caves of Bermuda afford equally conclusive evidence of 

 subsidence. Many of these now occupy a level considerably 

 below that of the sea, and consequently receive a large in- 



*Thomson : " The Atlantic," I, p. 320. 



