Correspondence—Gerard W. Williams. 95 
this area were ignorant of Dr. Falconez’s own definitions of the two 
types of granite. 
Finally, as the district was traversed in 1911, why are not these 
Saben Garri granites mapped as “‘ projections of younger granite ”’ 2 
They cover a larger area than the Kila granites, which are correctly 
mapped! Can it be that since Dr. Falconer adopted the theory 
(vide last paragraph in his letter) that tin occurs only in the younger 
granites, and since the presence of tin im situ in the Sabon Garri 
granites is unquestioned, he has rechristened these rocks to suit 
the theory ? 
It is easy to say in what rocks a given mineral does occur, but 
he would be a foolish man who asserts in what rocks it will not occur. 
Mineral occurrences are not confined to one age, and Murchison’s 
classic error in regard to the occurrence of gold should not be for- 
gotten. This is a matter of considerable importance. If tin is found 
only i in the “‘ younger granites’, then it would be idle to look for it 
in any of the other rocks, so that, vide Dr. Falconer’s map, only a 
very small area offers any prospects for the miner. 
When I found tin occurring in granites which agreed with 
Dr. Falconer’s description of the archeean granites associated with the 
eneisses (and mapped as such by him), I traced one series of these 
rocks and differentiated them from the normal non-stanniferous 
type under the name of the Sabon Garri granite. 
Believing in the importance of this observation I published it, 
hoping that other mining men would come forward and describe the 
country with which they were familiar. By so doing the slight 
knowledge we have of the stanniferous granites would be widened. 
Nigeria is a large country, and vastly important as Dr. Falconer’s 
work has been, it is only an outline of the geology of the Protectozate. 
The details, if they are to be filled in, must be done by the men on the 
spot who bring forward their notebooks and samples. The mining 
man is usually fitted to do this work. As a class unacademic in 
training or thought we make academic errors unconsciously. Witness 
the premature description of the “‘ younger”’ granites as Mesozoic 
in my own“ Notes”’. But on the whole the mining engineer who has 
preserved his interest in geology makes a good “* unskilled labourer ”’ 
in the field of geology, capable of recording observations and bringing 
home samples for the benefit of those whose knowledge is infinitely 
greater but whose opportunities of travel are vastly less. It is 
in that capacity that I regard my own work, a record of things 
seen, but not in any way an attempt to raise controversies. 
I am sure that the Curator of the Sedgwick Museum would gladly 
give Dr. Falconer access to any of the slides or specimens so that he 
may see for himself the types of rock described, especially Nos. 100 
and 105. 
GERARD W. WILLIAMS. 
P.O. Jos. 
November 27, 1920. 
