AND PORTO SANTO. 141 



I do not think our present knowledge of the comparative anatomy 



of timbers is sufficiently advanced to determine'. The sand is 



calcareous, whether from the destruction of fragments of the 



transition Umestone (found beneath the basalt at St. Vicente) in 



the bed of the ocean, or from comminuted shells, I will not venture 



to pronounce, although I incline to the former opinion. The 



carbonate of lime in the sheaths or envelopes of the wood, bears a 



greater proportion to the silex than in our common mortar, than 



which their substance is much harder; for estimating it by the 



difference of weight after the escape of the gas, it amounted to 43 



per cent. There is much ferruginous sand, mixed with that thus 



thrown up, resulting from the destruction of the masses of red tufa 



constantly falling from the chffs into the sea. On the western 



limit of this local deposit, are large globules of basalt (which from 



their concentric form and other appearances have evidently been 



in a fluid state), laying loose upon the soil, from the tufa (in which 



they are still found imbedded at greater heights) having been 



washed away from them. On such a soil the vegetation must be 



wretched ; a mesembri/anthemum and an orobus were the only 



plants that existed, or rather languished there. 



Having described this locality to the best of my ability, I leave 

 abler geologists to draw the conclusions ; but perhaps I may be 

 allowed to submit : — First, that it has evidently been an irruption 

 of the sea, from the heaps of terrestrial shells mingled with the 

 marine, and from the trees being found standing on their roots, 

 and not deposited promiscuously in detached fragments, or flat- 

 tened, as they would be, had they been transported thither, or 

 had they been subjected to any pressure of a superincumbent 

 stratum, afterwards removed. Secondly, it is clear that this must 

 have happened after the Atlantic had lost that considerably higher 



' Specimens of these lignites have been sent to the Geological Society. 



