292 SCIENCE IN SHORT CHAPTERS. 



are subangular. They differ from the Gal way boulders in 

 being chiefly basaltic instead of being mainly composed of 

 carboniferous limestone. Some of these at Dunluce are 

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

 carboniferous limestone. I had not at hand the means of 

 positively deciding this. 



Neither could I find any unquestionable examples of 

 glacial striation among them, though at the upper part I 

 saw some lines on boulders that were very suggestive of 

 partially obliterated scratches. 



On looking at the cavern walls surrounding me the 

 theory so obviously suggested by the boulders on the floor 

 was strikingly confirmed by their structure and general 

 appearance. The imbedded "bombs" are subangular, and of 

 irregular shape and varying composition, 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 glacier 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 un- 

 equivocal volcanic bomb; no approach to anything like 

 those described by Sir Samuel Baker in his '"'Nile Tribu- 

 taries of Abyssinia," the miniature representatives of which, 

 ejected from the Bessemer converter, I 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 of an inner crater of Mount Vesuvius. These as 

 they fell upon the ground around me were flattened out 

 into thin cakes. There was no approach to the formation 

 of subangular masses, like those displayed upon the Dun- 

 luce cavern walls. 



Some years ago a project for melting the basaltic rock 

 known as " Rowley Rag," and casting it into moulds for 

 architectural purposes was carried out near Oldbury, and I 

 had an opportunity of watching the experiment, which was 

 conducted on a large scale at great expense by Messrs. 

 Chance. 



It was found that if the basalt cooled rapidly it became 



