3fay 1 6, 1872] 



NATURE 



43 



cyanides and nitriles. An article on inorganic analysis, 

 by Bunsen's flame reactions, will be i'ound of great interest, 

 and will repay a considerable study. In fact, the whole 

 volume is most complete, and must be looked on with 

 great satisfaction. A. P. 



OUR BOOK SHELF 



Indi-x- tier Pctrographie mid Stratii^raphic der Schwciz 

 nnd Hirer Uingebiingen. Von B. Studer, Professor der 

 Geologic. Pp. 272. (Bern : K. Schmid. London : 

 Williams and Norgate ) 



Twenty years having elapsed since the publication of the 

 " Geologic der Schweiz," Prof Studer thinks that some 

 new account of the geology of his country cannot be 

 deemed superfluous. Since the date of that work nume- 

 rous separate volumes, papers, maps, &c., relating to the 

 geology of Switzerland have appeared. Many of these, 

 however, are diflicult of access, and not a few have been 

 to all intents and purpDses lost sight of As a conse- 

 quence of this, it is exceedingly difficult or even impos- 

 sible for the student of Swiss geology to find out what 

 has been written. This is easily understood when we re- 

 member that Switzerland has been .1 favourite field of 

 study with geologists of all nations, and that descriptions 

 of her rock-masses and formations are to be met with 

 in the publications of almost every scientific society in 

 Europe. Prof. Studer complains, and not without reason, 

 that many of the names of rock-divisions and formations 

 are derived from little obscure outlying places, for which 

 we look in vain on the best maps, or from fossils which 

 are familiar to only a few adepts, and that the same rock 

 or formation, as the case may be, is known by different 

 names in different regions, thus giving rise in the student's 

 mind to confusion worse confounded. This index ('the 

 preparation of which must have cost its author a world of 

 labour) will smooth the way to learners, and will, we are 

 persuaded, be of scarcely less value to professors them- 

 selves. Petrological and stratigraphical synonyms are 

 clearly explainecl, and the equivalents of the Swiss rocks 

 met with in adjoining countries are given. The inde.^c is 

 arranged alphabetically, and the list of "articles" leaves 

 nothing to be desired. The descriptions are short, clear, 

 concise, and at the same time comprehensive, those 

 which relate specially to Swiss geology being of course 

 the fullest. The author modestly says that his index 

 makes no pretensions to be a text-book, and refers his 

 readers for greater details to the works of Naumann, 

 Zirkel, Senft, Cotta, &c. ; yet we think that the very ab- 

 sence of minute details will be one of its chief recom- 

 mendations to the geologist, who can always turn to the 

 text-books and other sources when he feels inclined, for 

 the index literally bristles with references. A long list of 

 localities is added, by consulting which we are referred to 

 the various articles in which they are mentioned. Thus, 

 with a good map and Prof. Studer's index before him, one 

 may gather a very clear conception of Swiss geology. 

 The book is not bulky, and will be an invaluable com- 

 panion to any geologist who thinks of trjing his hammer 

 in the "playground of Europe." J. G. 



On the Early Stdi^cs of an Ascidian (Cynthia pvrifonnis). 



By Edward S.' Morse, Ph.D. (Boston : 1S71.) 

 In this communication, reprinted from the Proceedings of 

 the Boston Society of Natural History, Dr. Morse gives 

 an account of his examination of the tadpole-like larva 

 of a sessile Tunicate at Eastport, Maine, in July 1870. 

 He confirms the statements of Kowalcwsky and Kupffer, 

 and describes "a remarkable structure in the caudal fin, 

 which vividly recalled the fine diverging rays seen in the 

 embryo fish. These rays were exceedingly delicate. 



though plainly marked. They ran off nearly parallel to 

 the longitudinal axis of the tail, and were confined to the 

 last five segments." This observation, if confirmed, will 

 be of importance ; it points rather to general piscine affi- 

 nities in the Tunicata than to their special connection 

 with Anitliioxus. We are gild to see that Dr. Morse is 

 alive to the danger of mistaking the effects of preserving 

 fluids for natural appearances in microscopic specimens. 

 Some neat figures illustrate the paper, which we hope is 

 only the beginning of more complete investigation of this 

 deeply interesting subject by the writer. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his corespondents, Mo notice is taken of anonymous 

 communications. ] 



Magnetism in Copper Slags 



Ox examining the magnetic properties of some ores and 

 mineral.'!, I observed that a specimen of ore furnace slag from 

 copper smelting was strongly polar magnetic. 



Being surprised at this phenomenon, I mentioned it to Dr. 

 Percy, Professor of Metallurgy at the Royal School of Mines, 

 who kindly gave me permission to examine some of his sLags, 

 and also some of those exhibited in tlie Geological Museum. 



I examined several specimens of ore furnace slags, and found 

 they were all more &r less magnetic and strongly polar ; this even 

 extended to some very small pieces the size of a pea. Most of 

 these were of the ordinary kind, and of a porphyritic appearance, 

 from tile [lieces of white quartz imbedded in their mass. 



One .specimen was of a vitreous character. This was not so 

 strongly magnetic as the ordinary kind. 



Metal slab's from the second fusion. — Those examined were 

 polar magnetic. They were Museum specimens, beautifully 

 ciystallised ; the magnetic properties were distinct throughout 

 the mass, though more feeble than in the ore slags. 



Roaster slags from the third fusion. — I examined two speci- 

 mens of this class ; both were polar magnetic, but the magnetism 

 was confined to a few points, and A\as not developed in the 

 whole mass, resembling the consequent points in magnetism, i 



Refinery slags. — I examined one specimen ; it was very feebly 

 magnetic, though not polar, and the magnetism was confined to 

 a few points in the mass. 



In the analysis of copper slags, the iron present is always esti- 

 mated as protoxide in combination with silica, forming a silicate 

 of protoxide of iron. Unless this silicate is magnetic, it is diffi- 

 cult to understand how the whole of the iron is thus combined. 

 Further analysis must decide this point. 



Edmund F.- Mondy 



The Volcanoes of Central France 



Geoldc.ists state that the volcanoes of Auvergne have not 

 been in action in historic times (see Lyell, last ed., p. 479 ; also 

 Jukes and Geikie, p. 354). I find, however, that the Rogation 

 Days were appointed by Mamercus, Bishop of Vienne, in Gaul, 

 about A. D. 460, lor the purpose of chanting litanies to stay the 

 volcanic eruptions which were then devastating his diocese (see 

 Robertson's ".Hist. Ch. Church," 4th eJ., vol. i. p. 5S9 ; also 

 "Proctor on Book of Common Prayer," note, page 251.) 



Youghal, Co. Cork, May 13 W. J. Green 



The Eruption of Vesuvius in 1855 



It has occurred to me that, at the present moment, the sub- 

 joined extract from the travelling notes of my husband, the late 

 Dr. Marshall Hall, might be thought worthy of insertion in your 

 valuable periodical. We happened to be at Naples when the 

 eruption of Vesuvius in May 1S55 occurred, of which the 

 following gives some description : — 



"During five years Vesuvius had remained in a state of in- 

 activity, when, on May i, 1855, indications of an eruption mani- 

 fested themselves. 



" Early on the morning of the 1st smoke and fire appeared. 



