650 



CRATER OF LAGOA. 



[Ch. XXIX. 



Professor Heer, of Zurich, has since published (1855) an account 

 of some additional fossils collected by M. Hartnng from the turf of 

 San Jorge, enumerating twenty-seven forms, referable to ferns and 

 phenogamous plants, most of them agreeing with species now inhabit- 

 ing Madeira, such as Pteris aquilina, Trichomanes radicans, &c, and 

 leaves like those of Osmunda regalis (?), no longer found in the island. 

 Among the dicotyledonous plants the Professor describes Myrica 

 Faya, Greodaphne fwtens, Erica arborea, &c, also a few genera, such 

 as Corylus and Ulmus, now foreign to Madeira. The botanical de- 

 terminations both of Prof. Heer and Sir C. Bunbury would lead us to 

 refer the leaf-bed to a period as modern as the Newer Pliocene, if not 

 the Post-pliocene.* 



The lignite above mentioned and the leaf-bed occur at the height 

 of 1000 feet above the level of the sea, and are overlaid by super- 

 imposed basalts and scoria?, 1100 feet thick, implying the existence 

 of an ancient terrestrial vegetation long before a large part of Ma- 

 deira had been built np. The nature of the tuffs accompanying the 

 lignite, together with some agglomerates in the vicinity, entitles us to 

 presume that near this spot a series of eruptions once broke out. 

 Nor is it improbable that there may have been here the crater of 

 some lateral cone in which the lignite and leaf-bed accumulated ; for, 

 although craters are remarkably rare in Madeira, when we consider 

 how great is the number of cones of eruption, yet on the mountain 

 called Lagoa, 2-J miles west of Machico, a crater as perfect as that of 

 Astroni near Naples may be seen. 



At the bottom of this circular cavity (fig. 70*7), which is about 



Fig. T07. 



Crater of 



2-J- miles west of Machico, Madeira. 



In this cut, taken from a sketch of my own, the depth of the crater may appear 

 too great, unless it is borne in mind that there are no trees visible, and most of the 

 bushes are of the Madeira whortleberry ( Vaccinium Madeirense), five or six feet 

 high. Immediately behind the foreground an artificial mound is seen thrown up as 

 a fence. 



* Heer, Schweiz. Gesellschaft fur Naturwissenschaften, Band XV. 



