60 EXCURSIONS IN MADEIRA 



S. 7° W., and, within, (a little northwards of the centre, and about 

 35 feet below the brink) is an aperture about 25 feet long, and 15 

 broad, through which you see the sea ; the walls of the caverns 

 resounding with the rush of the waves entering below. The 

 depth of this vast marine well, a term which I merely hazard for 

 the moment, as conveying a better idea of its position and ap- 

 pearance than any further description could, is about forty-five 

 feet. This rent, apparently too considerable to be attributed to 

 the mere elastic force of confined vapours, presents every evidence 

 of having been formed by a minor volcanic heave, which threw up 

 vast blocks of the rock it rent from beneath the ocean, to form a 

 passage, but did not eject any lava or contents of its own. For 

 both the basalt rock in which it is formed, and that of the vast 

 masses which are scattered at the mouth of the aperture, are 

 highly scoriaceous, and present the strongest traces of fusion on 

 the surface. The elliptical wall which rises thirty-five feet above 

 this fearful aperture, and forms the greatest circumference of the 

 funnel, is of tufa, dipping to the south, and which, yielding more 

 easily, has been undermined, and has fallen in to a greater extent, 

 from the same heave which rent the stubborn rock beneath it ; the 

 shock having spread as it proceeded upwards through these looser 

 and softer strata. The compact basalt, which covers the tufa in 

 many instances, is wanting in the present, and the nearest coulie 

 of it inland, or behind this aperture, diverges from it, and may be 

 traced to the sea without approaching it, so that no superincum- 

 bent weight could have contributed to the falling in of the tufa. 

 There is not the smallest trace of any ejection from the aperture 

 having streamed over the waU of tufa, indeed there is not the 

 smallest evidence of any thing having been thrown or forced up, 

 but masses of the rock which was rent by the heave. Some of the 

 masses of porous and scoriaceous basalt scattered near this aperture, 

 are thinly coated with chalcedony. The Loo rock may have 



