Geology i and Climate of the Island of Madeira. 353 

 the beach in the little bay or landing place. The structure of 

 the plant thus sanded up he thought to be replaced by carbo- 

 nate of lime from the percolation of water ; the lime possibly 

 supplied by the decomposition of the shelly fragments. 



To these, or any of the explanations that have been oftered, 

 various objections might be made ; but the chief difficulty left 

 unremoved by them, seemed to me the accounting for the vast 

 ([uantity of calcareous matter in the formation ; far more than 

 the lime borne along with an irruption of the sea, or resulting 

 from the decomposition of the scattered specimens of shells 

 could possibly supply. For not merely the fossils, but the great 

 mass of the sand-formation in which they lie is calcareous. 



Calcareous deposits, similar to that of Madeira, have been 

 described by voyagers as occurring at the Cape of Good Hope, 

 and in New Holland. Of the latter, the most recent account is 

 given by Mr Darwin in the valuable and interesting volume 

 recently published, containing the observations in Geology and 

 Natural History, made in the expedition of H. M. Ship Beagle. 

 In speaking of Van Diemen's land, he says :* " One day (March 

 J 836) I accompanied Captain Fitzroy to Bald Head, the place 

 mentioned by so many navigators, where some have imagined 

 they saw coral, and others petrified trees, standing in the posi* 

 tion in which they grew. According to our view, the rock was 

 formed by the wind heaping up calcareous sand ; during which 

 process, branches and roots of trees, and land shells, are en- 

 closed ; the mass being afterwards consolidated by the perco- 

 lation of rain-water. When the wood had decayed, lime was 

 washed into the cylindrical cavities, and became hard. The 

 weather is now wearing away the softer rock, and in conse- 

 ([uence the casts of roots and branches project above the sur- 

 face. Their resemblance to the stumps of a dead shrubbery 

 was so exact, that, before touching them, we were sometimes at 

 a loss to know which were composed of wood, and which of cal- 

 careous matter." 



I have examined the accounts given by former travellers of 

 this place. It was Vancouver who first observed it in 1790* 



* Journal of Kesearches, &c., by Charles DarTvin> Et>q. Sec. Geological 

 Society* London, 1839, p. o37> 



