552 MADEIRA. 
fourteen degrees was observed ; but it was local, and varied much in 
a short distance. 
At Brazen Head, the eastern cape of the harbour of Funchal, the 
following were the alternations of beds observed, beginning above :— 
24 feet—Hard grayish and bluish-gray compact basaltic rock, scoriaceous above and 
below. 
6 feet—Tufa; red and columnar, immediately under the overlying basalt, but yellow 
below. 
32 feet.—Tula; fine-grained, soft and friable, with 14 feet of pumiceous conglomerate 
near the middle of the bed. 
2 feet.—Pumiceous tufa. 
44 feet.—Tula ; fine, friable, ash-coloured. 
feet.—Ibid. 
3 foot.—Pumiceous tufa. 
~] 
for) 
feet.—Tufa, fine ash-coloured. 
feet.—Pumiceous tufa, coarser above. 
~~ oO 
feet.—Tufa ; fine ash-coloured. 
35 feet—Compact basalt similar to the uppermost bed. 
The whole height is one hundred and twenty-nine feet; of this, 
seventy feet are tufaceous, and lie between two layers of basaltic rock. 
The seventy feet of tufa are divided into four layers of well-defined 
limits. The prismatic structure of the upper part of the first layer of 
tufa was quite regular. The prisms were two to three inches thick, 
and about three feet long ; above, they had a deep brownish-red colour 
and some lustre; below they gradually changed to a yellowish-red 
shade, and were less hard. ‘The structure is the result of the heat 
communicated by the superincumbent layer when first ejected. The 
change of colour to red, owing to the heat depriving the oxyd of iron 
of its water, had taken place in many parts of the island where exa- 
mined by us. 
The upper basaltic layer has a rough, scoriaceous look above and 
below, while the interior is very compact, and it resembles thus many 
of the subaerial ejections of recent volcanoes. 
To the east of the place where this section was observed, the layers 
overlap the hill, saddle-like. From the gradual change in the dip 
along the coast, and the character of this hill, it seemed probable that 
there had been a point of eruption in the vicinity. 
Dikes.—Dikes are frequently met with over the island, wherever 
the rocks are uncovered. Several were observed along the path lead- 
ing in and out of the Corral, some of which appeared to cut through 
