PREFATORY REMARKS. xi 



sions to be drawn from the subfossil statistics ; for it is in the 

 Madeiran archipelago alone that the Heliciferous deposits 

 (whether calcareous or muddy) have been accurately defined (as 

 regards their extent and character), and systematically investi- 

 gated ; and although it is true that beds of a similar nature 

 exist in the other Groups also, they have not there been pointed 

 out, or localized, with equal precision, and it is to be feared 

 that many of the forms which have been reported, from time to 

 time, by travellers, as ' subfossilized,' were founded upon 

 examples which were merely dead and bleached, and which, in 

 point of fact, were not obtained from any deposits which could 

 be looked upon as truly subfossiliferous ones. In the Madeiran 

 archipelago, on the contrary, the beds are both well known and 

 rigidly circumscribed, and may therefore be safely reasoned upon 

 in discussing the geological structure of the islands ; and, al- 

 though in reality there may be more of them than those with 

 which we have hitherto become acquainted, it is only from three 

 regions, up to the present date, that the strictly subfossil speci- 

 mens are recognized, — namely (1) Porto Santo, {2) near Canical 

 in Madeira proper, and (3) on the extreme summit of the 

 Southern Deserta. So uniform however is the geological con- 

 formation of these various sub- African Groups, that we may feel 

 tolerably confident that the same arguments which apply to the 

 Madeiras will apply with an almost equal amount of truth to 

 the others. 



Teignmottth. Oct. 1], 1877. 



