CORRESPONDENCE. 
GEOLOGY OF THE NINGI HILLS. 
Sir,—I hasten to express my regret that I didnot mention the fact 
that in 1911 Dr. Falconer mapped the Ningi-Kila—Fagam granites. 
I am afraid that I am so familiar with and indebted to ‘The 
Geology and Geography of Northern Nigeria” that I forgot that 
others might not be equally acquainted with it. 
I do not understand what is meant by “local controversies ”’. 
So far as I know Dr. Falconer is the only geologist who has written 
anything on the geology of this area, and also I do not see how these 
preliminary notes, based on a prospector’s notebook, can be regarded 
as controversial. It would have been better, | admit, to have 
retained Dr. Falconer’s non-committal nomenclature of the “‘ younger 
granites ’’, at any rate pending further research. 
It is, however, difficult to follow the rest of the letter. In the map 
that accompanies Dr. Falconer’s book the area covered by my 
traverse is, with the exception of the Ningi, Kila, and Fagam Hills, 
entirely mapped as ancient crystalline rock, as part of the oreat 
mass of archzean rocks that form the basal plain of Northern Nigeria. 
I have not the book by me at present, as lam on trek, but lam lemme 
certain that, as shown on the map, Dr. Falconer’s itinerary passed 
up from Sabou Garni, through Tipchi, and thence to the Ningi Hills. 
Ii passes therefore over the area | mapped as Sabon Garri granites, 
and along tlie same rocks in the shadow of the great mass of Duchin 
Chanya Cherigi. 
It was on this authority that I classed these granites as archean, 
for in all respects they correspond with the archean granites 
described in the book, notably in that they show ill-defined margins 
with the gneisses and never, like the “‘ younger granites ’’, show any 
contact alterations. If, then, my Sabon Garri granites are merely 
‘““a number of outcrops of younger riebeckite granite projecting 
through older micaceous gneisses of various types’, they should, 
according to Dr. Falconer, be accompanied by well-defined contact 
alterations. But there is no sign of such alteration, and though 
Nos. 100 and 105 were taken close to the edge of the mass and near to 
the schists and gneisses, they show no sign of marginal cooling. No 
one looking at these rocks and those of the Ningi granite could fail 
to note the marked difference in structure. 
Moreover, these Sabon Garri granites may be traced across the 
Minna River and up to Ningi. Two miles north of that village there 
is an excellent contact between the Sahon Garri and the Ningi 
granite. The latter displays chilled margins and the usual contact 
phenomena. 
I fear that the “‘ capable observers who repeatedly traversed ”’ 
