62 TEST ACE A ATLANTIC A. 



the breaking-up of the intermediate land, it is tolerably cer- 

 tain that an enormous period must have elapsed since the shells 

 which are now either deeply imbedded or are else scattered 

 loosely over the surface were in a living condition. Yet in no 

 single instance have they been transformed into 'fossils' (as 

 usually understood by that term), being strictly, and merely, sub- 

 fossilised. 



Whatever be the history of these singular beds, 1 it is quite 

 clear that they have a direct bearing on the geological struc- 

 ture, and former configuration, of the islands ; and therefore in 

 tabulating their contents we must do so with the utmost cau- 



1 It has always appeared to me that the drift sand of which the Canical 

 beds, and so many of those in Porto Santo, are mainly composed is strictly of 

 a marine nature, in fact similar to that of the present beaches, with which 

 some of them are in almost immediate proximity ; for the broken-up frag- 

 ments of sea shells, well distinguished by their solidity and sculpture, abound 

 in it everywhere, and the spines of Echini are also far from uncommon. 

 Moreover, although I have not myself observed it, a microscopic Polystomian 

 was mentioned by Mr. Lowe (Prim,., Append. XV., note) as being not more 

 rare, in the Canical deposits, than it is in the sand which forms the neigh- 

 bouring beach. Heer therefore was decidedly in error when he asserted that 

 no Polystomians had been observed in its composition, and that the sand 

 contained exclusively the triturated remains of Terrestrial Mollusks. No 

 doubt the latter occur to a prodigious extent, and may perhaps add largely, 

 when ground down and afterwards decomposed by the action of the elements, 

 to the calcareous matter which binds together considerable portions of the 

 surface and has enabled the infiltrations which have followed the course of 

 various roots and branches to assume definite and often the most grotesque 

 shapes, standing out, when the loose surrounding drift has been gradually 

 blown away from them, like (what might almost be regarded, at first sight, 

 as) the fossil remains of a former copse or wood. But that these trunk- and 

 root-like concretions (formed of varying proportions of earth and sand sol- 

 dered together, as it were, by a calcareous cement) have been slowly accu- 

 mulated around the different parts of shrubby plants (which perhaps were 

 washed down, along with the shells, by overwhelming torrents, from a higher 

 altitude) is rendered all the more probable from the fact that when broken 

 open they will generally be found to be longitudinally hollow in the centre, 

 as though the stems and roots which were originally enclosed had perished, 

 leaving only the clumsy masses which had been solidified, more or less per- 

 fectly, around them. But, be this as it may, the sandy portion itself seems 

 to me to be entirely marine, blown up, in a great measure, from the beach, 

 towards which this particular conchyliferous district uniformly slopes. 

 Nevertheless, on the other hand, the deep layers of somewhat indurated but 

 friable earth with which the calcareous incrustations are here and there 

 commingled, and which more or less teem with land-shells (whether whole 

 or fragmentary, and seldom much thickened or solidified), a large proportion 

 of which are characteristic of the sylvan regions of a lofty elevation, now totally 

 disconnected with this low tongue of land on which the Canical beds are placed, 

 point unmistakeably to the action of sudden and violent floods, which must 

 have carried them down, accompanied frequently by the remains of birds, to 

 well-nigh the level of the shore, and that too at a period when the configura- 

 tion of the adjoining country was very different from what we now observe it to 

 be. So that two counter processes would appear to have been concerned in 

 the elaboration of these singular deposits, namely, the washing down of 

 material from the mountain habitats above, and the gradual drifting up of 

 the marine sand from the beaches beneath. 



