108 



Lieut. Nelson on the Geology of the Bermudas. 



Ireland.— The position of this island is similar to that of St. George's ; but owing to its narrow- 

 ness (in one place, Cockburn's Cut, the breadth being hardly fifty yards) there is little room for 

 the development of the saddle-shape ; although I conceive that a reference to figs. 5, 6, will show 

 that however now truncated, it once existed. 



Fig. 5, section east end of the island, and Fig. 6, section at right angles to a, Fig. 5. 



Fie. 5. 



h. a.f. i. h, medium stone, c. soft sandy bed passing into h. g. d. 



Fig. 7. 



d. e. g. hard rock. 







i ( 



Caverns under stratum d, fig. 5, and covered with red earth I. 



Although, as before stated, a species of helix occurs in all the strata, not merely imbedded, but 

 filled with a hard stone, yet in this island there are six or seven marked divisions in the section, 

 showing different deposits of red earth (fig. 5), similar to that on the surface, not only in compo- 

 sition, but in being deposited in the rude troughs formed by the abraded basset edges of the 

 strata. The rock above d is uniform in structure and texture, and thus contains the best quarries ; 

 that below it, is generally rubbly and short-grained, varying constantly from a hard limestone to 

 loose sand; below this bed also, numerous caverns (b,) have been opened during the progress of 

 the fortifications ; and, with but very few exceptions, whenever they are perfect, they contain salt- 

 water, having their bottom below the sea level. In every instance except one (fig. 8. p. 112), the 

 red earth lies almost immediately on the roofs of these hollows, fig. 7. I, 



Ireland is remarkable for having the finest quarry of building materials in the whole group. 

 The stone of the eastern half consists of fine and coarse particles of comminuted shells or corals, 

 hard subcrystalline limestone, and masses of corals imbedded in compact or granular limestone. 

 The softer varieties prevail from Cockburn's Cut, westward. 



Alluvium. 



All that can be noticed under this head is the blacky rich, tenacious mud of 

 the marshy districts ; it has obviously much of a vegetable nature, and makes 

 an excellent garden soil when mixed with the red earth. 



By different measurements which I have taken, the Mangrove Swamp and 



