1908-9.] ON THE ORIGIN OF THE CANADIAN APATITES. 497 
IV. The evidence supplied by certain associated minerals whose 
uniform presence is thought to have an important bearing on the subject. 
In the following pages each of these classes of evidence is con- 
sidered in detail, adding to the facts already published such new material 
as appears to throw additional light on the question. 
ee 
EVIDENCE OF THE ROCKS. 
6. All the Canadian apatite deposits occur in those series of rocks 
known as the Grenville and Hastings. When these were first mapped, 
and for many years after, they were considered a part of the Laurentian 
system. ‘hey are enclosed by the gneisses of ‘‘the basement complex”’ 
and are difficult to differentiate from each other and the surrounding 
rocks, but it became increasingly evident that below the lowest of these 
and above the ‘‘fundamental gneiss’ there was a very definite break. 
The geologists of the then newly developed uniformitarian school believing 
they saw in the schistosity of the granite gneiss the marks of an original 
bedding naturally concluded that above the unconformity the clastic 
nature of the rocks was beyond dispute. 
7. The reaction from this extreme uniformitarianism led to the 
claim that not only the ‘‘basement complex,’ but also the Grenville 
and Hastings are eruptive. Since then the general trend of geologic 
opinion, in the light of increasing data, has been turning again in the 
other direction. 
8. One of the most recent investigations into the natures of the 
Grenville and Hastings rocks was that undertaken by Barlow and Adams 
and described in the Canadian Geological Survey Report for 1896.5 
These investigators made a careful examination of the area of contact 
between these two series and the true Laurentian, and have given their 
reasons for believing the Grenville to be clastic. ‘‘In the region under 
examination, it comprises a great development of limestones, with which 
are associated certain gneissic rocks whose minute structure and appear- 
ance mark them as highly altered sediments.”? ‘The reasons which 
led them to these conclusions Were as follows: 
(a) The investigations of Dr. Adams showed these rocks to be very 
different from the prevailing types of granitic and dioritic gneisses. 
8 Barlow and Adams, Geol. Surv. Can. Summary. 1896: 45 
9 Idem.p. 47. 
