AND PORTO SANTO. 6S 



Beyond the fort and village are one or two alternations of the 

 basalt and red tufa, the former being uppermost ; and this leads 

 to the lofty cliffs composed of a basalt with horizontal fractures, 

 which sometimes appears, from decomposition, to be imbedded in 

 red earth, and is covered by shallow, cork-like layers of tufa. All 

 these cHffs have no doubt been produced by the combined attacks 

 of the ocean and atmosphere. The deeply incHned planes, na- 

 turally created by volcanic streams flowing from a central and 

 elevated crater to the sea, were first worn away by its waters at 

 their base ; shallow vertical depths being formed in the first 

 instance, the sea continued to undermine, whilst the atmosphere 

 decomposed, and the crumbling summits of these cUffs being, from 

 the continvied action of the sea below, gradually brought to over- 

 hang the base, avalanches ensued, which increased their face or 

 depth. Close to the Cabo Garajao, the basalt descends consider- 

 ably, and the deposit of tufas above it becomes very deep. East 

 of the Brazen Head, there are several basalt dikes descending 

 through the tufa, some of which have evidently been formed before 

 the shps ; and the basalt in some places presents a series of con- 

 centric circles, as if it had formed a small whirlpool when in the 

 fluid state. It seems very evident, that these dikes are in no 

 instance injections of basalt from beneath, but have been formed 

 by streams filling up those cracks and gaps in the tufa, created by 

 the convulsions preceding an eruption, and by the sUps resulting 

 from the partial giving way of former deposits. In descending 

 from Pico Euivo, I saw two dikes (5000 feet above the sea) uniting 

 above, like the prongs of a pitch-fork, which it would be difficult 

 to explain, but as a downward stream. The tufa, in the vicinity 

 of these dikes, is naturally harder and firmer than that to the west- 

 ward. We next pass Santa Cruz, which Ues in a fine break, 

 uninvaded by the streams of the upper basalt, with Pico Camacha, 



a Uttle to the west of its bed, Pico jVIoraynya, (beautifully wooded) 



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