Geology^ and Climate of the Island of Madeira. 357 



nic agency. The extinct species of sliells, and other appear- 

 ances (such as a fragment of an extinct monocotyledonous vege- 

 table, apparently a Lycopodium, found by Mr Smith) presented 

 on the surface of the formation, shew that its age is b'^fore the 

 latest part of the tertiary epoch. If this account of the mat- 

 ter be correct, I think the difficulty is satisfactorily removed 

 as to the enormous amount of calcareous matter (the origin of 

 which Mr Bowditch and others have had to account for by 

 such inadequate causes as the comminuted sand of distant 

 limestone beds, or the decomposition of the shells scattered on 

 the surface of the ground), for the Alcyonia would give from 

 their own structure all the carbonate of lime which appears ; 

 and, indeed, in many places, the coral may be seen in every 

 stage of decomposition, the specimens everywhere crumbling 

 down into the amorphous soil of calcareous matter of which 

 great part of the surface of the formation is already composed. 



Thus far an induction from observed facts seems to lead. 

 Whether the coral be an extinct species, or the Alcyonium ar- 

 horeum : whether the formation be similar to those with which 

 it has been classed, or of a nature not elsewhere as yet ob- 

 served : how there come to be found on the surface such a vast 

 number of land molluscse : "' and various other questions, — re- 

 main for future investigation. 



Between St Jorge and St Ann's there appears a bed of lig- 

 nite, on the bank of the river of St Jorge, immediately before 

 the entrance of a stream called the Ribeiro de Tabaco. Sr. 

 Mousinho describes it as lying above a bed of hard clay im- 

 pregnated with lignitic matter, which rests immediately on 



* It has been observed that calcareous rocks have more influence than 

 any others in increasing the number and propagation of molluscap- (See Ed- 

 ward Forbes' Report, p. 128, in Transactions of British Association for 

 1839.) The presence of this calcareous tract in a country almost wholly ba- 

 saltic, may account for the remarkable accumulation of shells in this spot, 

 while they occur scattered rarely in the rest of the island. 



Mx Bowditch wa« wrong in stating tlint marine shells occur here. Mr 

 Lowe states (Primitifc Fauncc et Fionc Madorensis, Camb. Trans., vol. iv, 

 p. C4), " Nullam quidcm specicni mnrinam cum illis (terrestribus) commix- 

 tam vidi. Dclph inula sulcata (Bowd. Excursions, p. 140^ est Heliris spc* 

 cies (H^ delphiuulu Nob)." All the couIchI sbellb are ttiTestrial f^peciea* 



