628 



NA TURE 



[October 22, 1908 



The whole subject of trade diseases is in fact too 

 larg^e and too complicated to be handled by a single 

 author, and it cannot be dealt with in generalities. 

 The facts are difficult to come by and hard to inter- 

 pret, yet it Is upon accurate detail alone that preven- 

 tive measures, involving as they may do such large 

 interests, may with propriety be undertaken. Dr. 

 Oliver has provided a very pleasant introduction to 

 the subject, which should at any rate tend to promote 

 cordial relations with his Continental confreres. 



A. E. B. 



SCIENTIFIC EXPLORATION IN DAHOMEY. 

 Mission scieiitifique au Dahomey. By Henrv 

 Hubert. Pp. iv -1-568. (Paris: E. Larose, 1908.) 

 Price 15 francs. 

 TN this work M. Hubert gives a very detailed de- 

 -L scription of the results of his various journeys in 

 Dahomey, dealing principally with the meteorology, 

 the action of surface waters and of the sea, and the 

 geology. The volume is accompanied by an admir- 

 able geological map on the scale of i : 1,250,000, 

 giving the broad structural features of the colony as 

 far as Sansan-Haoussa, on the Niger, in appro.xi- 

 mately 14° N. lat. It is, of course, idle to expect 

 «ntirely satisfactory conclusions at a comparatively 

 «arly stage of investigation, but there is every 

 reason to congratulate M. Hubert on the volume he 

 has produced, on which much time and care have 

 been lavished, and which constitutes a great advance 

 in our knowledge of West African geology. M. 

 Hubert mentions at the outset the characteristics 

 well known to geologists on that coast, of a general 

 simplicity of the main features, a complication in 

 detail and a woeful scarcity of fossils. 



As was already known, crystalline rocks occupv 

 by far the greater part of Dahomey, and the coarse 

 granitoid gneisses, banded gneisses, mica- and horn- 

 blende-schists, granites and pegmatites do not 

 greatly differ from those of Kamerun and southern 

 Nigeria. 



Amongst the less common rock-types described 

 may be mentioned an alkali-granite containing 

 riebeckite, recalling the similar rocks described from 

 Zinder and south of Chad; and some cipolins from 

 the bed of the Zon (Savaloo region), associated at 

 Zompa with a scapolite-hornblende-gneiss. In a 

 somewhat brief account of the petrography these 

 cipolins are described as containing diopside, forsterite 

 and calcite, the first and second occasionally altered 

 ?nto antigorite. 



Omitting for a moment the recent beds, M. Hubert 

 finds the continuity of this great stretch of crystalline 

 rocks is broken twice; first by the quartzites of the 

 Atacora ridge, and secondly by the grits of the Gourma. 

 The Atacora range traverses the colony obliquely 

 from Kirtachi, on the Niger, to about the tenth 

 parallel; and is, in M. Hubert's opinion, a prolonga- 

 tion of the northern and southern range, forming 

 the central part of Togo Land, which twists south- 

 westwards to reach the sea at Accra. 



Additional information concerning the relations of 

 NO. 2034, VOL. 78] 



the .Atacora quartzites to the underlying gneiss and 

 mica-schists would have been welcome, and we may 

 incidentally remark that the word quartzite is used 

 throughout the book for somewhat dissimilar rocks. 

 The Atacora quartzites are probably quartz-schists, 

 and when disturbed (they are generally horizontal) 

 are folded with the underlying rocks. On very 

 slender evidence M. Hubert provisionally maps these 

 rocks as Silurian. 



The Gourma grits occupy a tract of countr\' much 

 smaller than, but mapped as essentially parallel to, 

 the Atacora range. The rocks extend from Kodjar 

 to a point more than 100 kilometres south-westwards. 

 These Gourma grits are surrounded by crystalline 

 rocks, noteworthy for the abundance of basic types, 

 both amongst the schists and the eruptive series. 

 In regard to age M. Hubert places these grits 

 between the Atacora quartzites and the far more 

 recent beds of the Niger basin, considering them 

 nearer to the former than to the latter. 



It is interesting to note the resemblance they bear 

 to the Bandiagara and Hombori beds recorded by 

 M. Desplanges. 



Between the Gourma grits and the alluvium, 

 " terre de barre," and other deposits now in process 

 of formation, two areas are noteworthy as contain- 

 ing comparatively recent beds, and as helping 

 towards a reconstruction of West African geography 

 in late Cretaceous and Tertiary times. These are 

 the grits of the Niger basin and the calcareous beds 

 of Lama, which form a narrow strip crossing the 

 colony obliquely to the south of Abomey in 7° N. 

 lat. The ages of these deposits are not definitely 

 fixed; the Niger beds are unfortunately unfossil- 

 iferous, and the fossils of the Lama region are not 

 sufficiently characteristic to allow the Eocene age, 

 suggested for them, absolutel}' to be proved. The 

 identification is based on the occurrence of a Turi- 

 tella, near to T. esclii, which in Kamerun is asso- 

 ciated with undoubted Eocene fossils, and on the 

 occurrence of Dactylopora cylindracea, Lamk. A 

 photograph of a specimen of the shelly limestone and 

 the general habit of the beds recalls the ( ? Upper) 

 Cretaceous beds of the eastern province of southern 

 Nigeria, and it appears at least possible that future 

 investigation may show the Dahomey rocks to be 

 rather older than was at first believed. 



The very interesting question of the age of the 

 Niger grits has to be left entirely open. They form 

 the plateau on either side of the river between 

 Sansan-Haoussa and Gaya, and have been cut 

 through by the Niger, which thus exposes the crystal- 

 line rocks beneath. M. Hubert notices these beds as 

 occurring as far south as Sakassi, in northern 

 Nigeria, and somewhat similar rocks occur on the 

 Jebba-Lokoja section of the river. Is it possible that 

 these beds also are of Cretaceous age ? 



Nearly one-third of the book is devoted to a dis- 

 cussion of the meteorology and the action of super- 

 ficial waters, while a few short chapters are con- 

 cerned with the distribution of animal and vegetable 

 types. Distribution of races as determined bv geo- 

 graphical conditions greatly interests M. Hubert, and 



