chap. tii. Superficial Calcareous Deposit. 163 



when the stone on each side contains particles of quartz, 

 is entirely free from them : hence we must suppose that 

 these layers, as well as certain vein-like masses, have 

 been formed by rain dissolving the calcareous matter 

 and re-precipitating- it, as has happened at St. Helena. 

 Each layer probably marks a fresh surface, when the, 

 now firmly cemented, particles existed as loose sand. 

 These layers are sometimes brecciated and re-cemented, 

 as if they had been broken by the slipping of the sand ' 

 when soft. I did not find a single fragment of a sea- 

 shell ; but bleached shells of the Helix melo, an existing 

 land species, abound in all the strata ; and I likewise 

 found another Helix, and the case of an Oniscns. 



The branches are absolutely undistinguishable in 

 shape from the broken and upright stumps of a thicket ; 

 their roots are often uncovered, and are seen to diverge 

 on all sides ; here and there a branch lies prostrate. 

 The branches generally consist of the sandstone, rather 

 firmer than the surrounding matter, with the centra 

 parts filled, either with friable calcareous matter, or 

 with a substalagmitic variety ; this central part is also 

 frequently penetrated by linear crevices, sometimes, 

 though rarely, containing a trace of woody matter. 

 These calcareous, branching bodies, appear to have 

 been formed by fine calcareous matter being washed 

 into the casts or cavities, left by the decay of branches 

 and roots of thickets, buried under drifted sand. The 

 whole surface of the hill is now undergoing disintegra- 

 tion, and hence the casts, which are compact and hard, 

 are left projecting. In calcareous sand at the Cape of 

 Good Hope, I found the casts, described by Abel, quite 

 similar to these at Bald Head ; but their centres are 

 often filled with black carbonaceous matter, not yet 

 removed. It is not surprising, that the woody matter 

 should have been almost entirely removed from the 



