158 



THE GEOLOGIST. 



Mr. Cox has laudably determined that the contents of the cave shall not be 

 broken up nor disturbed, anticipating the probability of its being honoured with a 

 royal visit. 



Polar Forces and Clbavagb : Centres or Creation.— X. Y. Z. (Dublin). — 

 " Sir, — If it would not be trespassing too much on your kindness, would you 

 favour me with answers to the following, through the medium of your monthly 

 paper The Geologist ? — It has always seemed to me that geologists, in speaking 

 of polar forces, in reference to cleavage, only sMft the difiSculty by giving it a 

 name, as I have never been able to understand what they mean when they use this 

 term, or how such forces could act effectually. Can you inform me under what 

 plea any geologist objects to there being only one centre of creation, and 

 requires more ? I cannot imagine, and have never been able to find anywhere 

 stated, what the necessity may be which renders it necessary to suppose more 

 than one. Lastly, perhaps you can suggest to me some elementary and, at the 

 same time, extensive and sound work on the previous of these two questions, viz., 

 cleavage." — The hypothetical application of polarity as an agent in the cause of 

 cleavage is not admitted now by most geologists, lateral pressure being the 

 fashionable doctrine. The well-known polar forces of electricity and magnetism 

 have been used hypothetically and by way of analogy by some authors, in 

 explanation of the changes which some of the old rock-masses have undergone, 

 and in reference to the formation of certain mineral veins. This subject has Ibeen 

 well treated by Mr. Robert Hunt, in the " Memoirs of the Geological Survey," 

 and by Mr. R. W. Fox, in the " Philosophical Transactions," and there is a 

 resume of the subject by the late Sir Henry de la Beche, in his " Greological 

 Observer." Mr. Evan Hopkins has given a very wide range to the probable action 

 of these so-called " polar forces." St. Helena, Galapagos Islands, Van Diemen's 

 Land, Australia, and many other instances might be adduced of the existence of 

 local faunas and floras, which it would be very diflBicult to understand if we were 

 to suppose there had been only one centre of creation. This subject is well treated 

 in Sir Charles Ly ell's " Principles of Geology," and, with respect to the floras 

 especially, has been well illustrated by the late Professor Edw, Forbes, in the 

 " Memoirs of the Geological Survey," Our correspondent's last question facetiously 

 reminds us of the old woman with bad eyes, who went to the Boston bookseller for 

 a new Bible of the largest print, smallest size, and cheapest price. The question 

 is, however, a very proper one, and we reply to all such with much pleasure. 

 Unfortunately there is no such collective work as X. Y. Z. requires on the subject 

 of slaty cleavage. Mr. H. C. Sorby and the late Mr. Daniel Sharpe have written 

 some admirable essays, and have done much in elucidation of this matter, and. 

 there is the first part of a report by Professor J. Phillips, in the " Report of the 

 British Association for 1857," in which a general review of what has been done is 

 commenced, and in which the chief labours hitherto made in this direction will be 

 found embodied. The last edition of Lyell's " Manual " contains a resume of 

 some of the later researches on this point, and Mr. Jukes, in his ** Manual of 

 Geology," lately published, ably treats of it in his chapter on Physical Geology. 



Elementary Works. — J. H. M. (Staines) asks what is the best elementary 

 geological work for a young man to study ? — Sir Charles Lyell's " Elements of 

 Geology," and " The Principles of Geology," by the same author, "The Wonders 

 of Geology" and "The Medals of Creation," by Dr. Mantell, are first-rate books. 

 The last edition of the " Wonders " being printed under the revision of T. 

 Rupert Jones, Esq., the assistant-secretary of the Geological Society, the newest 

 discoveries and latest determination of the science are in it engrafted on the 

 original labours of that late eminent geologist. Sir Charles Lyell, we all know, 

 brings every new edition of his two celebrated works completely up to the mark. 

 Other excellent works which occur to us are Page's "Text-book of Geology;" 

 Professor Ansted's " Geology ; " Professor Phillip's and Professor Jukes's 

 Manuals, and the late Sir Henry De la Beche's " Geological Observer." Miss 

 Zoruliu has written, too, some very pretty rudimentary books. 



Alloimiank.— Z. (page 116.)— Allophane occurs at New Charlton, near 

 NNoolwich, Kent, in chalk, and is of a white honey yellow, or red colour. That 



