320 
T. E. Bowditch, Esq. On the Geognosy of 
form. No part of this conglomerate effervesced ; but it was 
covered by a shallow horizontal bed of sandstone, of the same 
nature as that above the fetid limestone. 
Through all these different horizontal masses, that is, from the 
summit of the table-land, of which this island is principally 
formed, to the sea, a depth of about 240 feet, descend, more or 
less perpendicularly, numerous basaltic dikes; sometimes jut- 
ting out like walls, and serving as rude stairs in the ascent ; at 
others, nearly even witli the surface of the various rocks they 
intersect ; and frequently running parallel with the beach for 
some distance at the water’s edge, and forming into piers. In 
some parts, their surface was covered with considerable patches 
of a dull coralloidal carbonate of lime, and in the basalt of the 
dikes on the north side, (for it was the eastward face which af- 
forded me the section I have described), I found beautiful crys- 
tals of nepheline. In the dikes immediately north of Fas Juli- 
ana, I found a deposit of native alum. 
The limestone beneath the basalt of Madeira, is evidently of 
the same nature and formation as that beneath the basalt at 
Lisbon. The shelly limestone of Baxo is distinct from that at 
Almada on the Tagus ; but it is probably of the same forma- 
tion as the shelly limestone mentioned by Baron de Humboldt 
as covered by basalt, on the coast of Portugal. Of what forma- 
tion is the limestone found on the coast of Africa, opposite to 
Teneriffe ? And does that, subordinate to the tufa at Laneer- 
sta and Forteventuria, resemble either of those at Baxo * ? 
I made the height of the Peak 6164 feetf ; and I think it 
was impossible for the day to be more favourable. I had taken 
the angle of elevation of the Peak of Ruivo with a reflecting 
circle, from the point generally visited by strangers for the best 
view of the Coural, and adjoining the Pico des Bordes, know- 
® Humboldt’s Rel. Hist ., 1. 1. c. 2., and Supplement , p. 641. 4to. 
f Fortin’s Barom. 619.65, T. 9. 45, T. d. 9.45. C., 49. F., in the turret of Mr 
Veitch’s house in Funchal, 154 feet above the level of the sea, (allowing 7 feet for the 
rise of the tide at the syzygies, when the height of the turret was determined) 770.70, 
T. 20.5, F. d. 20.5. C, 69. F. T-T'=16»*, 2 : '—X 2 <(-f *')=103”2, correc . 
tion for latitude 8 W * 
