432 W. G. Foye — Nephelite /Syenites of Ontario. 



If the alkalies are neglected, the difference between the per- 

 centages of the other elements are not greater than those reg- 

 istered by the varying types of the nephelite syenites. 



Column 1 of Table II shows beyond doubt that solutions 

 high in alumina and relatively high in soda were introduced 

 into the limestone and that, to a degree, these solutions were 

 similar to the material which went to form the nephelite 

 syenites. 



To one who has studied the Haliburton district closely, it 

 appears very clear that the processes which Adams and Barlow 

 described have actually taken place and that amphibolites 

 have been derived on a large scale from limestone. All steps 

 in this process are continually met with. The limestone is first 

 impregnated with diopside crystals. Then scapolite and diop- 

 side appear side by side in a matrix of calcite. Later diopside 

 and feldspar are developed, and finally the diopside is replaced 

 by hornblende and the transformation is complete. 



The evidence of this transformation was accepted by the 

 International Committee on Pre-Cambrian nomenclature.* 

 The following statement is quoted from their report : 



" The committee are of the opinion that the evidence is indis- 

 putable that the granite bathyliths in this region change the 

 invaded limestone into a dark-gray amphibolite, which, together 

 with fragments of the interbanded amphibolites found every- 

 where in the limestone series, occur scattered throughout the 

 granite mass in the form of included fragments." 



The amphibolites are vastly more important areally than the 

 nephelite syenites, and hence the origin of the solutions 

 which left the granite magma and transformed the Grenville 

 limestones to amphibolites is of prime importance. The evi- 

 dence presented in this article shows a close genetic relation 

 between the amphibolites and the nephelite syenites. 



A study of the map published by Adams and Barlow and an 

 intimate knowledge of a portion of the Haliburton area war- 

 rant the following statements : 



(1) The area embraces some 3456 square miles, a fourth of 

 which is underlain by limestone and amphibolite and the re- 

 mainder by Laurentian gneiss and amphibolite. 



(2) A conservative estimate would show that the amphibolites 

 formed from 30 to 40 per cent of the limestone areas and from 

 10 to 15 per cent of the gneissic areas. 



(3) The contacts of large oval masses of gneiss with the sur- 

 rounding limestones usually are characterized by a zone of 

 amphibolite mingled with limestone. The average zone is one- 

 quarter to one-half a mile in width and represents a thickness 

 of from one to two thousand feet. 



* Report on Correlation of Pre-Cambrian Rocks, Jour. Geol., vol. xv, 

 p. 204, 1907. 



