338 GEOLOGY OF THE WEST INDIES. [Nov. 



islands; it appears, however, that the volcanic formation 

 ceases at Saba, and that Santa Cruz is composed of madre- 

 pore rocks at the west, and, on the eastern side, of rocks 

 similar to those of St. Thomas and St. Bartholomew. The 

 west end and the middle of the island, are low, and covered 

 with a shell limestone and madrepore rock. The founda- 

 tion on which this rock reposes is a stratum that retains 

 water, and may be a compact limestone, as the bases of 

 many of the little hills rest on solid limestone. The east 

 end is composed of different kinds of limestone, alternating 

 with amygdaloid, hornblend rock and porphyry, like the 

 rocks of St. Bartholomew; it is likewise hilly and broken, 

 being stratified in a direction nearly north and south. 



All the islands that have been described have a strik- 

 ing similarity both in their structure and the nature of 

 their materials; those that are partly or wholly covered 

 with the horizontal shell limestone, or madrepore rocks, 

 are exactly the same; those partly or wholly formed of 

 stratified rocks, consist of rocks more than half of which 

 are limestone, or have considerable quantities of lime in 

 tliem, and the remainder of the rocks differ very little; 

 they have nearly the same dip and direction; have a strong 

 characteristic mark of belonging to the transition class; 

 though from their deranged state, and the peculiar mode 

 of their decomposition, they differ a little in their appear- 

 ance from the transition rocks of Europe, for the lime- 

 stone is remarkably hard, dry and brittle, breaking into 

 sharp pieces, which sound like a bell, when struck with a 

 hammer: this may, perhaps, be the effect of the constant 

 heat of the climate. The different appearance which these 

 rocks as5:ume, when in a state of decomposition, from 

 those of northern latitudes^ may in part be attributed to 



