"CRATER XECK8" AND "VOLCANIC BOMBS." 291 



with the sources of eruption can occasionally be recog- 

 nized; they sometimes appear as masses of hard trap, col- 

 umnar or otherwise, projecting in knolls or hills above the 

 upper surface of the sheets through which they pierce." 



In other cases, the " neck " consists of a great pipe choked 

 up by bombs aud blocks of trap, more or less consolidated, 

 bombs which have been shot into the air and have fallen 

 back again. He then refers to one of these near Portrush, 

 and proceeds to state that the rock on which stands the 

 ruined Castle of Dun luce, "is formed of bombs of all sizes 

 up to six feet in diameter, of various kinds of basalt, dole- 

 rite, and amygdaloid firmly cemented, and presenting a 

 precipitous face to the sea." 



In a note dated September, 1877, Mr. Hull states that 

 subsequent examination, since the above was written, of 

 the rock of Dunluce Castle and the cliffs adjoining, has led 

 him " to suspect that we have here, instead of old volcanic 

 necks, simply pipes, formed by the filtration out of the 

 chalk into which the basaltic masses have fallen and slipped 

 down, thus giving rise to their fragmental appearance." 



Further on (page 14G) he describes without any sceptical 

 comment, "the remarkable mass of agglomerate made up 

 (as on the southern flanks of Slieve Gullion) of bombs of 

 granite, which have been torn up from the granite mass of 

 the hills below, and blown through the throat of an old 

 crater." Other geologists still adhere firmly to the bomb 

 theory, some ascribing the bombs to subaqueous rather than 

 subaerial ejection. 



Immediately under Dunluce Castle is a sea-worn cavern 

 or tunnel, which is about 40 or 50 feet high at its mouth, 

 affording a fine section of this curious conglomerate. The 

 floor of the cavern which slopes upwards from the sea is 

 strewn with a beach of boulders. The resemblance of this 

 beach to those I had recently examined at the foot of the 

 boulder-clay cliffs of Galway Bay (and described in a paper 

 read to the British Association), suggested the explanation 

 of the origin of the rock I am about to offer. 



In shape and size they are exactly like the Galway shore 

 boulders, those nearest the sea being the most rounded ; 

 higher up the slope, where less exposed to wave action, they 



