Ch. XXIX.] 



CRATER OF LAGOA. 



515 



smooth and un wrinkled, with a somewhat rigid and coriaceous texture, 

 and with undivided or entire margins. " These characters," observes Mr. 

 Bunburj^, " belong to the laurel-type, and indicate a certain analogy be- 

 tween the ancient vegetable remains and the modern forests of Ma- 

 deira, in which laurels and other evergreens abound, with glossy cori 

 aceous and entire-edged leaves, while below them there is an under- 

 growth of ferns and other plants." 



The lip'nite above mentioned and the leaf-bed occur at the height of 

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

 basalts and scoriae, 1100 feet thick, implying the existence of an ancient 

 terrestrial vegetation long before a large part of Madeira had been built 

 up. 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 considerable is the number of 

 perfect cones, yet on the mountain called Lagoa, 2J 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. 654), which is about 150 

 feet deep, is a plain about 500 feet in diameter, having a pond in the 

 middle, towards which the plain slopes gently from all sides. Such 

 ponds are often seen in the interior of extinct craters. Except in the 

 middle it is shallow, and supports aquatic plants. Many leaves must also 

 be blown into it from the surrounding heights when high winds prevail, 

 so that a mass of peaty matter convertible into lignite may collect here. 



Fig. 654. 



Crater of Lagoa, 2^ 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. 



Had streams of lava descending from greater heights entered this 

 Lagoa crater, they would have formed dense masses of compact rock 



