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KEFERENCE TO THE ORIGIN OF SPECIES. 



405 



remains (of Miocene date) already alluded to as having been 

 imbedded in the products of early eruptions. 



In Madeira the volcanic accumulations rise to the height 

 of 6,000 feet, and in the Grand Canary to 6,000 feet. The 

 hio-hest crater in Teneriffe rises to an elevation of more than 

 12,000 feet above the sea -level. 



We 



time 



from the history of the Canaries and volcanic archipelagos in 



Fig. 137. 





4 





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^Map of the Madeiran Archipelago. 



a. The Styx reef, 72 feet tmder water. 

 h. The Falcon reef, 26 feet under water. 



general, we may infer that v^hen one island is in a state of 

 unusual volcanic activity, the other adjoining islands enjoy 

 comparative repose. Moreover, in one and the same island, 

 different sets of vents have been in eruption in succession; as, 

 for example, in Madeira, where the series of cones which now 

 constitute the highest and central ridge, is not the most 



,f,?. 



