82 



PEOCEEDINGS OF THE GEOLOGICAL SOCIETT. [NoV. 22, 



pebbles, enclosed in a hard dark-red clayey matrix, of which (dis- 

 integrated) the abundant and highly fertUe soil apparently consists, 

 dry and fissured during the sultry season, but soft, tenacious, and 

 muddy during the heavy rains of the wet season. 



Beneath this, and forming the most marked, and apparently 

 the most abundant rock of the island, is a hard, tough, compact, 

 dark, dull-coloured, fine-grained basalt, which at some places, as at 

 Les Jumeaux, is distinctly columnar. Of this rock the most pro- 

 minent bluff's, cliffs, and off-lying rocks appear to consist (see map 

 and outHne, figs, 1 and 2). 



Fig. 1. — SJcetch Map of the Geology of Fernando Noronlia.] 



(;;£5;;;S) 









PgMtStMiQliacl, 

 xooiby.T 



l,jmj 



-/i 1^ ^ X 

 ' ' ' ■ ■-- 



Scale 



Ym Basalt. 

 ^^ G-ranite. 

 Tlie rest Conglomerate. 



The highest peaks of the group evidently consist of a fine-grained 

 light-grey granite, and notably Mount St. Michael, a huge, abrupt, 

 rounded, almost woodless islet, which is altogether granitic — and also 

 Fernando Noronha peak, situated about the centre of the north side 

 of the main island, near the convict village. This is a remarkable, 

 bold, inaccessible, needle-shaped prominence, 1014 feet high, which 

 protrudes through the conglomerate flanking its base. 



Large wave-worn masses of granite, and especially basalt, as well 

 as basaltic boulders from disintegrated conglomerate, lie plentifully 

 scattered along the fine yellow sandy beaches, especially at the chief 

 landing-place close to the Port Rock. Water, not over abundant, 

 muddy and brackish, is only found near the beach. 



It is a noteworthy fact that Fernando Noronhais 194 miles to the 



