June 8, 191 1] 



NATURE 



489 



tions are two which are here reproduced by permission 

 of the pubhshers. One shows a " sadd " sufficiently 

 solid to check the flow of the river and form a lagoon ; 

 in the other both steamers and sailing boats have been 

 brought up by a more compacted barrier of the same 

 kind. 



Khartoum is fully described, and the scientific work 

 carried on at the Wellcome Laboratories is referred 

 to. So many points of scientific interest are alluded 

 to, having a bearing on various branches of know- 

 ledge, that we can only regret that the results have 

 not a wider circulation and greater accessibility than 

 is afforded by the annual official reports. The founder 

 of the Wellcome Laboratory renders the results of its 

 staff available, but in forestry, hydrography, and also 

 in all that concerns the native races of the Sudan 

 those who are working there are gaining data which 

 have a value and importance beyond their own region. 

 The illustrations greatly assist in forming an idea of 

 the country described, but the map is not so satisfac- 

 tory; it would be of more use 

 if the modern place-names were 

 correctly given and a consistent 

 orthography employed. 



H. G. L. 



the reader and enhanced the value of the work as a 

 book cf reference if some plates had been included 

 sliowing the minute structure of the rocks. 



The book is technical and solely for the geologist, 

 and, though one would be loth "to lose any of the 

 excellent photographs with which the author'has em- 

 bellished his work, one ventures to think that in some 

 instances microscopy might have taken precedence. 



The granite intrusions (see Fig. i) arc pre- 

 Ct etaceous in age, and fall into two subdivisions : an 

 older foliated, and a younger non-foliated group, which 

 includes soda-granites. The pneumatolytic modifica- 

 tion of some of these granites, as at Bukuru, has as a 

 distinguishing feature cassiterite and sulphides of 

 copper, zinc, and lead. 



The Cretaceous beds, confined to parts of the valleys 

 of the Benue and its tributary, the Gongola, fall into 

 an upper and a lower series of grits and sandstones, 

 divided by a limestone-shale series of Turonian age. 

 It is interesting to note the presence of salt in the 



THE STRUCTURE OF 



HAUS ALAND AND ITS 



NEIGHBOURHOOD.' 



IF there is one point more 

 than another which calls for 

 the attention of the geologist in 

 West Africa it is the position 

 and age of the older sedimen- 

 tary series, i.e. the beds be- 

 tween the presumably Archaean 

 gneiss and the Cretaceous 

 strata. 



Such information as is avail- 

 able about these rocks, quartz- 

 ites and argillites, grits and 

 phyllites, is fragmentary, and 

 obtained from a variety of 

 sources throughout West 

 Africa, often frcim locilii i-s 

 where no recognised Mirvcy has 

 taken place, and where the 

 relations of the component 

 rock groups an' vmlcnown. 



On the wcsirin side (;l norlini'ii Xis;ciia we have 

 such a sediiiH'iilary sciics Irequenlly exposed, and witli 

 this Dr. l-'alc(in('i', in liis boolv, "'i'hc (ie()l()g\' and 

 Geography of Morllimi Nii4<'fi;t,"' Ii.as dr.ilt al Imt^ili. 

 He regards these rocks a^ the scairflx allcnd r, prc- 

 '<en(alivi-s of a gi'oup of ncIiIvi^ .hkI s. (liiiniiiarx 

 iriifis-^r-s li-iincil tlic "soldi" :' 11' I --.(•-• , lil'^all-^(■ ot 



Fig. I.— Exfoliation in the Killia Hills. From "The Geology and Geography of Northen 



l< \\n ^L^rii SI lies, and of veins of galena and blende 

 a! .\rohi. (ioiiliilcss connected witli a small inlier of 



i;iMnilr iir.ii I lie lown. 



S.ill o((iiis in ilii' norili-ra-niii jiart of southern 

 NiL;iiia, as (io al--o L;alrna and Mrinl,', whifll f.acts, 

 io;;ci|irr w i I h llic piiilialilr cxislrnr.' 1)1 'rui'oni.m Ix'ds 

 ill till' same iicighbourliood, suggest a general simi- 

 I. I ii \' ill lii~-ioi \ . 



ill I'l oh (iorates the Cretacrous b<^ds are pierced 



Mu'it" rclal i\-i-K- low- capacilx" lo|- n-i^liiiL', iTo-ion, ;iiul 



liclicvrs lliat tli<-\' wnc (|r|i< isiii-d upon a ^nrl.irr of l'\ dvl^i's .-nid vijjs of doli-ril 

 Af(dia'an c^m-i--- ilu' "li.ard" i_;nri^~- and .aflrclcd I >r. I- .i !c< >ii,i- l^^ ^onir -,iri'^-, i 



I horra I In' on l)\ ri'L;ion;il nii'laniofpliism , and ih) l>\ wliitli lie In \ist liclwern 



folding. JMM-.ni !..(;, w i>i tin- of <•. 



Il can scarcrK ho donlili-d llial llic i(iiaia/-sc|iis| ^ Kii^iin''- opini'Ui ilia! a [ta---^ 

 and (jiiaiiz-tnii^covitc-^chisls of Kahlia and llofin arc Xi^^nia lictwccn llic Mcsn/nii 

 the s;nne .-1^ those of the ("enlral I'l-ovinci of -.onlhein Tin |-e ,irc tiiicc Looiips ,.t I'jic.' 



\i:|ei-i.i, ;i cot-re|;if ion \\lii(di can pr<ihah!\- he eximd' (I XipVria, id w hiidi ih'' wesiiin onl\- ha- \-ii Idi d !os-,i|s; 

 to the roi h--, i.f fhi- Ivisii-rn rroxinc, and po-sih!- 

 for the 'MiLi-.d characdr ■■f I'w. ,. ■ rhi ! • !<■ eMcrdi; 

 C'r]isi:inf to olli.'i 



I )r. l'',dconer, ■: ■ d 



p.is-., has accoi'diiiL^h" ad-.aiM.d an : 

 siderahle inii)orl ;i ni-e, hiil it would I 



u ilh 



isilio 



•4 pl-'"' 



( I I 



U \]> I •■ 



wilh ef 



in I crest nu; : 1 1 1' 



I >| |i 1 rn^; iiion-- 



|)le\,llen| in cilh. I 



M (air 

 most 

 largely 

 mlv too 



NO. 2 1 71, VOL. 86] 



