172 



NATURE 



{Dec. 20, 1888 



Henslow has no reference to Beccari's remarks which 

 appeared in 1884 in the second volume of "Malesia" 

 under the head of " Piante ospitatrice.' In the preface 

 to the descriptions of his exceedingly beautiful and well- 

 known myrmecophilous plants, Beccari puts forward the 

 very view taken by Prof Henslow, both with regard to 

 floral and extra-floral nectaries, so that Prof Henslow has 

 no need " to venture to go further " {i.e. than Beccari), and 

 attribute the large honey-pits at the base of the leaf-stalk 

 oi Acacia sphccrocephala — see p. 157 — to the mechanical 

 irritation of ants. 



The book closes with some remarks on the origin of 

 species and the origin of flowers. There is evidence that 

 the author has not thoroughly acquainted himself with 

 some of the literature to which he refers, and in certain 

 instances important references are omitted altogether. 



THE CORAL REEFS OF THE PENINSULA OF 

 SINAI. 



Die Korallenriffe der Sinaihalbinsel, geologische und 

 biologische Beobachtungen. Von Johannes Walther, 

 Dr. Phil., und Privat-docent an der Universitat Jena. 

 Des xix. Bandes Atx Abhandlungen der Mathematisch- 

 physischoi Classe der K'dnigl. Scichsischen Gesellschaft 

 der Wissenschaften. (Leipzig: bei S. Hirzel, 1888.) 



MUCH has been written and said of late on the 

 origin of coral reefs ; yet the best authorities, 

 when they have not theories of their own to uphold, are 

 agreed in thinking that the matter is far from being 

 finally settled. For this reason a thorough examination 

 of all coral districts is much needed, and every work 

 which adds to the general stock of knowledge on the sub- 

 ject deserves attention. The present memoir deals with 

 the geology of the peninsula of Sinai, and the dependence 

 of the coral reefs in the Gulfs of Suez and Akabah on the 

 characters of the rocks forming the shores. Herr Walther 

 has undertaken difficult and disagreeable, if not dan- 

 gerous, journeys in the course of his research, and in 

 point of thoroughness his observations leave little to be 

 desired. Believing that a solution of the question in any 

 given area can only be obtained by carefully studying the 

 relations of the reefs to their basis, he has thoroughly 

 examined the geological character of the western moun- 

 tains of the peninsula, and gives in the first part of the 

 book a full account of all that he observed. The results 

 of his geological survey are most conveniently studied in 

 the plate giving a series of sections through the peninsula. 

 These show that south of Uadi Firan there are two paral- 

 lel lines of granite mountains, running north-west and 

 south-east, and between them lies a basin filled in with 

 sedimentary rocks. As far south as Gebel Nakus the 

 granite forms the shore, and the author points out that in 

 this region there is no fringing reef and no coral of any 

 kind. Further south, where the sedimentary rocks form 

 the sea-cliff, the fringing reef makes its appearance, 

 sending out offsets from the shore from place to place, 

 which form barrier reefs and even atolls. The shores of 

 the Gulf of Akabah are granitic, and are devoid of coral 

 reefs. Commenting on this, the author explains that 

 the granite is rapidly weathered out, and that its surface 

 thus constantly undergoing destruction does not afford 

 a sufficiently firm basis for coral growth. 



The coral reefs are divided into living reefs, sub- 

 fossil reefs, and ancient reefs. The first are the 

 fringing and barrier reefs or atolls actually being 

 formed beneath the sea-level ; the second are up- 

 heaved reefs, lying just above the sea-level, and con- 

 sisting of coral heads cemented together ; the third are 

 infrequent, and consist of masses of dolomitic lime- 

 stone, the structure of which betrays its coral origin, 

 lying 230 metres above the sea. The thicknesses of these 

 reefs were accurately determined, and were found to be, 

 for the ancient reef, 15-17 metres; for the sub-fossil 

 reef, 3-5 metres ; and for the fringing reef, 3 metres. 

 These facts are by far the most important part of the 

 author's work ; they prove that considerable changes of 

 level have taken place since the coral reefs were first 

 formed, and that these changes have been in the direction 

 of elevation. Thus another instance is added to the 

 many now accumulating of barrier reefs and atolls being 

 formed in an area of elevation. The slight thickness of 

 the reefs also deserves attention. At the end of the book 

 the author speaks of a reflux of the sea having occurred 

 rather than an upheaval of the land. As he does not 

 explain what he means by a reflux of the sea, his state- 

 ments are rather puzzling. Does he hold the view that 

 considerable changes of sea-level have occurred as conse- 

 quences of glaciation at either pole? In any case, the 

 phenomenon which he seeks to account for by an 

 alternating level of the sea, viz. the existence of a dead 

 reef below the sea-level and beneath the living fringing- 

 reef at Ras Muhdmmed, requires for its explanation nothing 

 more than a period of subsidence following on a period 

 of elevation ; and several of the geological facts seem to 

 point to a recent though slight subsidence at the southern 

 end of the peninsula. 



The author adds nothing to our knowledge of the bio- 

 logical conditions and the composition of coral reefs. His 

 accounts of the living coral and its mode of growth, of the 

 filling up of the interstices of dead coral blocks with 

 detritus, and the formation of oolitic granules, are familiar 

 to all visitors to coral lands, and have been fully 

 described by previous authors. Although an unnecessary 

 amount of space is devoted to the description of these 

 well-known phenomena, the whole work demands the 

 attention of geologists and of students of coral forma- 

 tions. The numerous plates and woodcuts render the 

 text light and easily comprehensible, and the map show- 

 ing the condition of the coral reefs at different geological 

 periods is of especial interest. G. C. B. 



OUR BOOK SHELF. 



The Book of the Lantern. By T. C. Hep worth, F.C.S. 



(London : Wyman and Sons, 1888). 

 The lantern has of late years become such an important 

 aid to almost every branch of education, even in theo- 

 logical and political matters, that no apology is needed for 

 the publication of a thoroughly practical treatise on every- 

 thing connected with it. As a former lecturer at the Royal 

 Polytechnic Institution, and present lecturer at the 

 Birkbeck, Mr. Hepworth has gained the practical experi- 

 ence the benefits of which he now places at the disposal 

 of others. 



After brief reference to the history of the lantern, the 

 optical arrangements are considered, and these are 



