Mr. J. Smith on the Geology of Madeira. 173 



The coal or lignite occurs on the north side of the island, on the 

 banks of one of the tributaries of the St. George. Professor John- 

 ston considers it to be the dried relict of an ancient peat bog, and 

 its lustre, compactness and rhomboidal fracture to be due to the ac- 

 tion of the basalt which overlies it. An analysis gave 



Carbon 60*7 



Hydrogen 5*82 



Oxygen and nitrogen .... 33*47 



99-99 



and 2005 per cent, of ash. This is the organic constitution of true 

 peat ; but no peat exists at present in Madeira, nor as far as Mr. 

 Smith is aware, has any been noticed so near the equator. He there* 

 fore suggests that this deposit may indicate a former colder climate 

 in that latitude. 



The sands of Canical are found near the eastern extremity of the 

 island, in a valley which extends from the northern to the southern 

 shore ; and they consist of small particles of basalt and comminuted 

 testacea, enclosing vast numbers of land shells as well as calcareous 

 incrustations of plants. The shells have been most carefully ex- 

 amined by the Rev. Mr. Lowe, and one sixth ascertained to belong 

 to species not now found living in the island ; the Canical sands 

 therefore are assigned by Mr. Smith to the Pleistocene or newest 

 tertiary sera. The calcareous incrustations have been considered by 

 some observers not to be of vegetable origin, in consequence of the 

 general absence of organic structure ; and Dr. Macaulay is of opinion, 

 from their consisting of carbonate and phosphate of lime, silica and 

 animal matter, that they are of animal origin, and probably belonged 

 to the family of Alcyonidce. As however they are mere casts, Mr. 

 Smith conceives that an analysis cannot throw light on their origin ; 

 and as all of them bear the most perfect resemblance to trunks or 

 branches, and one of his specimens exhibits impressions externally 

 of cellular structure, he has no doubt of their being the calcareous 

 casts of plants. 



In one of the small islets adjoining Porto Santo is a bed of fos- 

 siliferous limestone, which supplies the kilns of Funchal. The 

 fossils consist almost exclusively of casts, but Professor Agassiz 

 having been enabled to identify some of them with casts of recent 

 species, Mr. Smith infers that the limestone is an extremely modern 

 formation, though it has all the characters of primary marble. In 

 this case, the volcanic action, Mr. Smith states, was evidently sub- 

 marine, as the contact of the basalt and the limestone is so intimate 

 that the two rocks never separate when a mass composed partly o 

 each is detached by force. The elevation of the islet above the 

 level of the sea has not, however, disturbed the horizontal position: 

 of the beds. 



On the island of Porto Santo the volcanic action was sub-aerial, 

 as the basalt is scoriaceous on the surface, and rests on volcanic 

 brick. In this island there is a sandy deposit similar to that at 

 Canical. The Disertas, lying about three leagues to the south-east 

 of Madeira, Mr. Smith describes as a chain of volcanic mountains 



