276 SCIENCE IN SHORT CHAPTERS. 



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 Dimluce, " is formed of 

 bombs of all sizes up to six feet in diameter, of various kinds of 

 basalt, dolerite, 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 Dunltice 

 Castle and the cliffs adjoining, has led him " to suspect that we have 

 here, instead of old volcanic necks, simply pipes, formed by the 

 nitration out of the chalk into which the basaltic masses have fallen 

 and slipped down, thus giving rise to their fragmental appearance." 



Further on (page 146) 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 sec- 

 tion of this curious conglomerate. The floor of the cavern which 

 slopes upward 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 are subangular. They differ 

 from the Galway boulders in being chiefly basaltic instead of being 

 mainly composed of carboniferous limestone. Some of these at Dun- 

 luce are granitic, and a few, if I am not greatly mistaken, are of car- 

 boniferous limestone. I had not at hand the means of positively de- 

 ciding this. 



Neither could I find any unquestionable examples of glacial stria- 

 tion among them, though at the upper part I saw some lines on 

 boulders that were very suggestive of partially obliterated scratches. 



On looking up at the cavern walls surrounding me the theory so 

 obviously suggested by the boulders on the floor was strikingly con- 

 firmed by their structure and general appearance. The imbedded 

 " bombs" are subangular, and of irregular shape and varying compo- 

 sition, and the matrix of the rock is a brick-like material just such as 

 would be formed by the baking of boulder clay ; the inference that I 

 was looking upon a bank or deposit of glacial drift that had been 

 baked by volcanic agency was irresistible. 



I was unable to see on any part of the extensive section, or among 

 the fragments below, a single specimen of an unequivocal volcanic 

 bomb ; no approach to anything like those described by Sir Samuel 

 Baker in his " Nile Tributaries of Abyssinia," the miniature repre- 

 sentatives of which ejected from the Bessemer converterl have figured 

 and described in Nature, vol. 3, pp. 389 and 410, where Sir Samuel 

 Baker's description is quoted. 



I have witnessed the fall of masses of lava during a minor eruption 



