42 



Ascension. 



PAET I. 



towards the SE., whence the trade- wind blows. 1 This 

 structure no doubt has been caused by the ejected 

 fragments and ashes being always blown, during erup- 

 tions, in greater quantity towards one side than towards 

 the other M. Moreau de Jonnes has made a similar 

 observation with respect to the volcanic orifices in the 

 West Indian Islands. 



Volcanic bombs. — These occur in great numbers 

 strewed on the ground, and some of them lie at con- 

 siderable distances from any points of 'eruption. They 

 vary in size from that of an apple to that of a man's 



No. 3 



Fragment of a spherical volcanic bomb, witb the interior parts coars°ly cellular 

 coated by a concentric layer of compact lava, and this again by a crust of finely 

 cellular rock. 



body : they are either spherical or pear-shaped, or with 

 the hinder part (corresponding to the tail of a comet) 



1 M. Lesson, in the ' Zoology of the Voyage of the " Coquille "' 

 (p. 490), has observed this fact. Mr. Hennah (' Geolog. Proceedings,' 

 1835, p. 189) further remarks that the most extensive beds of ashes 

 at Ascension invariably occur on the leeward side of the island. 



