434 



NA TURE 



[March 12, 1908 



Werner restriclcd the use of the term by making the 

 hornblende-orthoclase rock of the Planenschen-grund, 

 near Dresden, the type of the class ; and now geolo- 

 gists are agreed in retaining the term for rocks with 

 granitic structure but of intermediate composition, con- 

 taining little or no free quartz, and having orthoclase 

 as their predominant felspar. Rocks of this class do 

 occur at Aswan, as shown by Dr. Ball, but they 

 appear to be in all cases subordinate to the true 

 granites with w hicli tlicy are associated. 



The chief rocks quarried at Aswan, both in ancient 

 times and also recently, for the construction of the 

 dam, are these granites, sometimes coarse-grained 

 and porphyritic, at other times fine-grained. Both 

 hornblendic varieties and types of these rocks rich- in 

 mica occur, and bv the diminution of proportion of 

 the quartz and the increase in abundance of the 

 subordinate plagioclase, the rocks pass locally by in- 

 sensible gradations into syenites and diorites. 



Full descriptions with excellent figures (plates iv. 

 to xi.) are given bv Dr. Ball, not only of these 

 plutonic tvpes, but also of the various metamorphic 

 rocks, and of the rocks that form dykes cutting 

 through both metamorphic and plutonic masses. The 

 survey has, of course, given the author abundant 

 opportunities for collecting specimens, of which he 

 has made ample use. Like Prof. Bonney, who 

 examined a series of the .Aswan rocks collected by 

 the late Principal Dawson in 1886, Dr. Ball is struck 

 with the general resemblance of the metamorphic and 

 igneous rocks, both of Upper Egypt and the Sinaitic 

 area, to the Archaean rocks of North America, and he 

 suggests that they may not improbably be of the 

 same great antiquity. The crushing and faulting of 

 these rocks with the intrusion of various dykes took 

 place, the author of this memoir argues, at a date 

 long subsequent to their formation, and this action 

 continued quite down to Cretaceous times, when the 

 Nubian sandstone was deposited quite unconformably 

 on their greatly denuded surfaces. Near the cataract 

 of Asvvan no remains of the Eocene clays and lime- 

 stones, found in other parts of Upper Egypt, occur 

 — they have probably been removed by denudation. 

 Subsequently to the Eocene period, there has been 

 elevation and great denudation. At this period of 

 elevation most of the faults which play such an im- 

 portant part, as shown in this memoir, in producing 

 the general features of the cataract area were formed. 

 By the denudation the older metamorphic and igneous 

 rocks w^ere exposed, and the escarpments and outliers 

 of Nubian sandstone formed. 



In the concluding pages of this interesting memoir 

 the author adduces evidence to show that the ancient 

 course of the Nile lay in a broad valley east of the 

 present river, and he discusses the problem of the 

 causes which have led to important changes in the 

 course of the river and the effects of these changes 

 on the character of the country. We must wait for 

 the extension of the geological survey of Egvpt, to 

 districts which at present remain untouched, for a 

 full solution of these problems. It is interesting 

 to learn that, although the site of the great Nile dam 

 was determined prior to the execution of the geological 

 NO. 2002, VOL. 77J 



survey, Dr. Ball is of opinion that the line actually 

 chosen for it was a satisfactory one, and that the 

 results of the survey do not indicate that any better 

 site could have been selected for it; and, further, that 

 the straight form, finally adopted for the dam, has 

 been at least equally successful in avoiding the difli- 

 culties presented by crushed and decayed rocks as 

 would the curved form originally suggested. 



J- W. J. 



THE " HISTOIRE INTI.ME " OF NITROUS 



OXIDE. 

 Das I.acligas: cine chcmisch-kiiltur-liislorisclie Studie. 



By Prof. Ernst Cohen. Pp. iv + 99. (Leipzig: W. 



Engelmann, 1907.) Price 3.60 marks. 

 ZLTABITUES of the Royal Institution, and especially 

 those who have interested themselves in its 

 early history, are aware of the existence of a 

 characteristically coarse caricature of Gillray's entitled 

 " Scientific Researches! New Discoveries in Pneu- 

 maticks ! Or an Experimental Lecture on the Powers 

 of .\ir," which first appeared in 1802, and is stated 

 by Wright and Evans, who published in 185 1 a de- 

 scriptive account of Gillray's cartoons, to represent 

 Dr. Garnett, the first professor of chemistry in the 

 Royal Institution, administering, with the aid of his 

 assistant, Humphry Davy, what is presumably laugh- 

 ing-gas to Sir John C. Hippesley, a noted patron of 

 the Institution and prominent as a manager, with 

 results disquieting to his " internal economy," and 

 disastrous to " That garment 'twere rude to do more 

 than allude to," as Thomas Ingoldsby says. 



This jirint is hardly so rare as Prof. Cohen would 

 seem to imply, and it has already done duty in con- 

 nection with the early history of the Royal Institution. 

 It — or rather what Prof. Cohen styles the right half 

 of it — is reproduced in Thorpe's biographical account 

 of Davy, published some years ago by Messrs. Cassell. 

 Prof. Cohen, apparently on the sole authority of Pictet, 

 who visited London in i8oi, and contrary to all con- 

 temporary evidence and the testimony of the editors 

 of Gillray's works, inclines to the opinion that the 

 person administering the nitrous oxide is Thomas 

 Young, who is styled professor of chemistry in the 

 Royal Institution, a position he never held. Of course, 

 a caricaturist like Gillray, who allowed himself un- 

 limited licence, and was bound by no rules either 

 of decorum or probability, might, in portraying a 

 wholly imaginary incident, commit any anachronism 

 he pleased. But there was no reason at the moment 

 why Gillray should be guilty of the anachronism of 

 putting Young into a position he never occupied, since 

 Garnett was the actual professor of chemistry when 

 Davv was assistant, and the humour of the incident 

 — such as it is — is in no wise dependent upon what 

 lecturer is behind the table. Pictet was certainly 

 present at a symposium on a certain Saturday even- 

 ing at the Royal Institution in the early summer of 

 1801, when, to quote from a letter from Davy to his 

 friend King at Bristol, " there was respiration, nitrous 

 oxide, and unbounded applause. To-morrow, a party 

 of philosophers meet at the Institution to inhale the 

 joy-inspiring gas. It has produced a great sensation 



