part 2] OF SOUTHERlSr ETEE PEIS'INSULA. Ill 



member, in order that a comparison with other rocks might be 

 afforded. A chemical analysis of an amphibolite from the gneisses 

 near Point Boston (hundred of Lincoln) was, therefore, made, and 

 this has already been set forth on p- 101, together with some com- 

 parative analyses. 



The amphibolite is placed witl other t3q3ical igneous rocks in a 

 well-defined subrang in the C. I. P. W. classification : namely, 

 II. 4.3.3, and, among the analyses quoted for comparison, it bears 

 the closest relation to the quartz-gabbro of Georgia. Chemical 

 analysis, therefore, is in harmony with the view that the amphi- 

 bolite is a metamorphosed igneous rock, perhaps most 

 comparable with a quartz-gabbro. 



The recent work of F. D. Adams & A. E. Barlow,i on the amphi- 

 bolites of the Laurentian area of Ontario, has shown that there 

 ;are certain amphibolites derived from the metamorphism of impure 

 calcareous or calcareo magnesic sediments, which are comparable 

 both chemically and petrographically with amphibolites of un- 

 doubted igneous origin. That amphibolites have been derived 

 by this process, there is in the Ontario region abundant field- 

 evidence ; for the rocks show that gradation of composition 

 which is at once characteristic of sediments, and the clue to their 

 origin. 



At Sleaford Bay there are metamorphosed impure dolomites, 

 consisting of diopside, bytownite, and microcline with scapolite, 

 and as inclusions in the Flinders gneisses, diopside-rocks of 

 undoubted sedimentary origin ; but, among these metamorphosed 

 calc-magnesian silicate rocks, there are none resembling in any 

 particular true amphibolites. This perhaps cannot be regarded as 

 conclusive evidence ; but negative evidence must here be con- 

 sidered an important factor. Moreover, there are no amphibolites 

 in the Flinders Series showing that variation of mineralogical 

 composition which is to be expected in amphibolites derived from, 

 calcareo-magnesic sediments. One of the important features of 

 large bands of the amphibolites is their uniformity of composition 

 throughout the mass, the reverse of which is the dominant 

 characteristic of the metamorphosed Sleaford sediments. 



For a like reason, any conception of the amphibolites which 

 represents them as sediments contaminated with basic volcanic 

 material utterly lacks evidence, and is in addition rendered very 

 improbable from the chemical composition. 



The conclusion is, therefore, enforced that these 

 amphibolites are in virtue of their chemical and petro- 

 graphic composition, metamorphosed igneous rocks of 

 slightly higher acidity than the normal gabbroid or 

 doleritic type of intrusive. 



The relationship of the analysed amphibolite with the igneous 

 rocks, quoted in the table on p. 101, may be illustrated by a gra]:)hical 

 representation of their anal^^ses, utilizing an adaptation of the O'^ann 



1 Mem. Geol. Surv. Canada, No. 6 (1910) pp. 104-16. 



