MADEIRA. Bt 
A columnar structure is of frequent occurrence over the island, 
though seldom perfect. One of the first places that strike the eye on 
entering the bay of Funchal, is a mass of oblique and curved columns, 
a short distance from the city, near Ilheo Rock. 
The tufas vary from a friable earthy rock to coarse conglomerates 
of scoria or pumice. Dark brown, brownish-black, yellowish-gray, 
ochreous and red, are the colours they present. Some varieties look 
like brick, both in colour, lustre and structure. Others are like loosely 
compacted earth. ‘The coarser kinds often contain imbedded grains 
of the several minerals above mentioned ; and at a locality near Ilheo 
Rock, (harbour of Funchal,) a friable yellow tufa afforded numerous 
small but perfect crystals of chrysolite, which were highly modified, 
and had a grayish-green colour. ‘The pumiceous bed examined was 
mostly made up of small fragments of pumice as large as a hazel-nut. 
Other conglomerates consisted of angular and rounded masses of the 
several varieties of basaltic rock and scoria. ‘The largest mass ob- 
served was about one hundred cubic feet in size. 
The varieties of rock described occur in alternating layers, and 
most of the cliffs and sides of the valleys present a regularly stratified 
structure. In a distant view, there is a striking resemblance to a cliff 
of secondary limestone ; the stratification was very uniform and dis- 
tinct, and nearly horizontal. This fact was exhibited with great 
perfection along the walls of the deep gorge called the Corral, where 
sections one to two thousand feet in height are exposed to view. Even 
isolated peaks, standing in this gorge, and rising toa great height, 
were stratified in the same manner, and the layers were equally 
regular, and as nearly horizontal. Pico Grande was of this kind; it 
is one of the loftiest peaks of the island, and owing to its singular 
castellated outline and isolated position, it is a peculiarly majestic 
sight on the descent to the Corral. The stratified structure is dis- 
tinct from top to bottom. In our rapid jaunt we had an opportunity 
to learn only that the alternations are numerous from compact and 
scoriaceous basaltic layers to tufaceous or conglomerate beds, of 
various colours, and coarse or fine in different degrees. Even the 
steepest precipices are faced with ferns and shrubs, which cling 
among the rocks; and on account of the luxuriant vegetation, much 
labour would be required to take down a correct account of the alter- 
nations of rock which constitute them. 
Although nearly horizontal, a slight dip to the southward was appa- 
rent, yet not exceeding three degrees. At one place an inclination of 
