226 bulletin: museum of comparative zoology. 



rock is generally readily recognized as such. It is formed in fairly thick 

 layers, from two to six inches, and always dips toward the sea at a very 

 moderate angle, and has nothing in cummon with the seolian strata 

 against which it abuts. Parts of it may be ground up again by a storm 

 should the calm between heavy surfs not continue sufficiently long for 

 it thoroughly to consolidate. 



All along the south shore one can find patches of beach rock dipping, 

 as observed by Professor Puce, to the sea at a slight angle, — the modern 

 beach rock of to-day, formed from the remodelling of the material thrown 

 up from the outer ledges. This beach rock is formed similarly to that 

 of the Florida Reef, where it plays so important a part in its economy, 

 while at the Bermudas it is of comparative insignificance. It is often 

 difficult to separate the beach rock from the base rock, but if, as I believe, 

 what is called " base rock " is only modified seolian rock, the latter has 

 not the importance attributed to it by Professors Rice and Heilprin. 

 On White Cliff Bay there are some seolian cliffs dipping at a sharp 

 angle into the sea, showing remarkably well the transformation of the 

 thin seolian layers into massive compact beds of base rock, in which the 

 dip of the strata can scarcely be detected, obliterated as it has been by 

 the cementing and solvent action of the sea water acting upon them. 



At Hungry Bay, Middleton Bay, and many points on the south shore, 

 and on the north shore at Ireland Island, and on the north shore of St. 

 George, there are numerous localities where it is possible to observe the 

 transition of the inclined or horizontal seolian strata above high-water 

 mark to the solid ringing limestone characteristic of the "base rock." 

 On the shore of Godet Deep to the west of Heron Bay, at the foot of 

 Gibbs Hill, the " base rock," can be seen passing gradually from the seolian 

 beds into the solidified ringing limestone characteristic of the intratidal 

 limits. The action of the sea cements the strata together, so that all 

 trace of their seolian structure is lost. In many cases, however, we can 

 trace the continuation of the seolian stratification indistinctly, so that I 

 am inclined to consider what is termed "base rock" as due merely to 

 such cementing action of the sea; the more so, as similar phenomena 

 are clearly observable all along the Cuban coast on the shore edge of 

 the elevated reefs between low and high water mark, where there is no 

 question of an underlying base rock. 



Professors Rice and Heilprin both speak of the "base rock" as dis- 

 tinguishing the old beach formation, and as indicating the position of 

 the former sea border. It seems to me that this basal rock is seolian 

 rock which has become excessively indurated by the action of the sea 



