182 PROCEEDINGS OF SECTION C. 



the final stages of consolidation, by issuing vapours and 



solutions rich in mineralisers. Thus at Heemskirk and 



North Dundas boron and, to a less degree, fluorine have 



attacked the minerals produced during the earlier 



stages of consolidation and the invaded rocks. At 



Anderson's Creek veinlets of scapolite within the aplite 



and pegmatite are attributable to the passage of chlorine 



through these masses. 



Turning now to those features of occurrence which concern the 



contact rocks themselves, a number of other important facts present 



themselves for consideration. 



These rocks are here called " contact rocks " for the reason 

 that they are, in some cases at least, characteristic of the contact 

 metamorphic aureoles which surround granitic invasions, and also 

 for the reason that they are, in the opinion of the author, certainly 

 to be regarded as genetically related to the observed acidic rocks 

 of the regions in which they occur ; yet certain reservations with 

 regard to the use of the term must be made^. 



It is undoubtedly necessary to make these reservations, 

 for the reason that contact rocks are usually regarded as being 

 zonally arranged with some marked degree of regularity about 

 the igneous rock causing the contact metamorphism and con- 

 formably with its boundaries. 



In those cases which are here under discussion no such arrange- 

 ment of the contact rocks is to be observed. In fact, the particular 

 contact rocks here described are to be regarded as arranged radially 

 rather than tangentially with respect to the igneous masses to which 

 they owe their origin. Nevertheless, since they are in essential 

 particulars identical with rock types which are known to be found 

 in other parts of the world within the zones of contact metamorphic 

 aureoles, as the result of the alteration of calcareous sediments 

 by the operation of the emanations from acidic magmas, the name 

 of contact rocks cannot be denied to them. 



The predominant structural feature of these rocks is the 

 lenticular or tabular form. That is to say, the contact rocks all 

 have a vein-like habit, when the whole of the mass of any develop- 

 ment is taken into consideration. And, where they are developed 

 within sedimentary boundaries, the veins or lenses do not always 

 coincide with the bedding planes of the enclosing rocks. 



It is particularly to be noted that these remarks apply only 

 to the rocks which are here being dealt with. There are other 

 contact rocks of more normal type surrounding the granite at its 

 immediate border, where the border has been observed, constituting 

 the normal tangentially-disposed aureole. The contact rocks 

 with which we are here specially concerned are found in the form 



1 It would perhaps be better if some modification of existing nomenclature were universally 

 adopted. Joseph Barrel 1, in writing of the geology of Marysvillc, Montana {U.S.A. Geol. Surv. 

 Prof- Paper No. 57, pp. 116 </ x«?.),usps the word "metamorphism " in treating of cases wherein no 

 change of composition in the altered rocks other than the expulsion of gas and water has taken place 

 and " metasomatism" where some alteration in composition is produced bv igneous emanations. The 

 contact rocks here discussed are considered to have been produced by the " metasomatism " of Barrell. 



