G. Poulett Scrope—Note on Mr. B. Mallet. 413 



on the cause of the occasional singularly perfect columnar configur- 

 ation of basalt and other volcanic rocks. It may suffice to say that, 

 so far as the present writer can understand it, as given in an abridged 

 form, it differs in no particular from that which was furnished by 

 himself fifty years back, in the first edition of his work on Volcanos 

 (ed. 1825, p. 135), and subsequently repeated in the second edition 

 of 1862 (p. 96). 



On one minor portion of this paper I am however desirous of 

 offering a comment at present, because it involves a mis-statement 

 of fact of some little importance towards the formation of just ideas 

 on the problem in question, — a mis-statement which is quite astound- 

 ing when it would have been easy for Mr. Mallet to ascertain the 

 truth, and so avoid the error into which he has fallen. It has refer- 

 ence to a portion of Mr. Mallet's theory on which he appears most 

 specially to pride himself as wholly original, viz. that of the formation 

 of those curious cup-shaped or ball-and-socket cross joints, sometimes, 

 but very rarely, found in basaltic columns. 1 " This solution," he 

 says, " is believed to be the first ever presented, which completely 

 accounts for the production of the very remarkable cup-shaped joints." 

 (p. 182, line 22.) 



Mr. Mallet's " original " solution of the problem is not very clear ; 

 but this is of the less consequence, inasmuch as it is founded on an 

 assumption, or rather assertion, which is untrue, viz. that the con- 

 vexities of the joints always point in the same direction, away from 

 the surface at which the cooling commenced. In this he is wholly 

 mistaken. 



It is the fact that the protuberances are found to occur indifferently 

 in both directions side by side in the same mass of columns ; and 

 of this fact Mr. Mallet might have convinced himself any day by 

 simply examining the group of basaltic columns from the Giant's 

 Causeway, which, as a member of the Geological Society, he 

 must have frequently passed in their rooms. This group consists of 

 three columns, figured in Mr. Woodward's paper, page 346, Vol. VIII. 

 of the Geological Magazine. Now it is perfectly evident that in 

 all of these three columns the direction away from the cooling sur- 

 face at which the splitting commenced must have been the same, and 

 yet in the very upper layer of this specimen the top surfaces of the 

 three columns are alternately convex and concave. Still further, upon 

 removing the first articulation of the left-hand column, it is found 

 to be biconcave, in the fashion of a double-concave lens, — the corre- 

 sponding convexities pointing of course both ways. So much for 



1 It is remarkable how rare these cup-and-ball-shaped joints in basaltic columns are. 

 They occur, as is well known, in the Giant's Causeway, and at StafTa ; though it is 

 by no means common in Scotland or Ireland. It is found in some of the basaltic 

 currents of Central France ; see the descriptions and engravings in Abbe Le Coq's 

 admirable work on that district, vol. v. But in Germany, notwithstanding the 

 number and perfect regularity of many ranges of columnar basalt to be seen there, 

 such joints appear to be wholly absent; since I am informed by my friend, Mr. J. 

 "W. Judd, at present on a geological tour in that country, that a single joint of the 

 kind from the Giant's Causeway in the Museum at Dresden is the only example 

 known among the German geologists he has met with, and is looked upon as an 

 extraordinary phenomenon. 



