70 EXCURSIONS IN MADEIRA 



is applicable to the shallow, ribanded beds of tufa by the water 

 side, which are not likely to have been washed down (by the 

 excessive rains or inundations which generally accompany volcanic 

 eruptions), and deposited precisely in the same quantity or direc- 

 tion, at different eruptions, and under circumstances differing 

 in some, if in no great degree p. The deep beds of tufa in the 

 interior seem to have been deposited confusedly, just as they were 

 vomited from the crater; for I cannot reconcile myself to the 

 opinion, that such vast masses can have resulted from the pre- 

 mature decomposition of the scoriae, which still remain perfect, 

 and in distinct layers ; although this tufa may perhaps have been 

 vomited as detached matter, afterwards agglutinated by rains and 

 torrents. 



The next question is, are there any remains of the grand crater, 

 and where was it situated ? To the former part of the question 

 I would answer, no ; and to the latter, (recalling the directions of 

 the various streams and ridges of basalt, and their narrowness 

 and greater depth in that neighbourhood, from which they all 

 appear to have taken their departure) between the peaks of Ruivo, 



former is found to compose the cliffs by the sea side, the latter (and the various strata 

 we have described beneath it) must have given way, and sunk beneath the bosom of 

 the ocean. 



P That there was a considerable interval between the last, and the preceding eruption, 

 the streams from both of which must have destroyed all vegetation in their course, 

 seems evident, from the uppermost beds of tufa being found to contain fragments of 

 wood in different parts of the interior of the island. Of the wood found in the tufa 

 (200 feet above the sea) near Canigal, I merely saw a specimen for a moment, and that 

 in the hand of another person, but it appeared to me to have passed into woodstone 

 (holzstein, W.). In another specimen brought from the neighbourhood of the ice 

 house, (upwards of 4000 feet above the sea,) and which will be found amongst those 

 sent to the Geological Society, the wood, thickly imbedded in an indurated, compact, 

 red tufa, is still soft, and comparatively mialtered : it has evidently belonged to full 

 grown trees, and in its porous nature, and the distance of its fibres, seems to me to 

 resemble that of the draccena more than any other. 



