OBSERVATIONS IX EASTERN CANADA AND EUROPE. 189 



morphicj are in reality only different portions of one and the same mass. * * * As 

 a result of this summer's work, I think it may be safely concluded that the rocks com- 

 prising the principal area of anorthosite above referred to, as well as most, if not all, 

 of the smaller areas, are of eruptive origin." * 



He confirms this in his summary for 1888 in the following words : — 



" All the areas of anorthosite now known to occur in the district have been ex- 

 amined, and mapped, and have proved to be either eruptive masses cutting through 

 the gneisses, or masses interstratified with the latter, but probably still of eruptive 

 origin." f 



Callaway has shown, in his paper on the granitic and schistose rocks of 

 northern Donegal, that the granite-gneisses of that region, which have been 

 regarded as Laurentian and which correspond closely in lithological 

 characters and mode of occurrence with the Laurentian of Canada, are really 

 irruptive through older- rocks, which must have arched them over, and present 

 all the evidences of irruption which have been adduced by the writer in 

 support of the irruptive origin of the Laurentian northwest of Lake Superior. 

 He thus states his conclusions: — 



"1. The granite rock of northern Donegal, originally supposed to be the result of 

 the metamorphism of sediments, and recently referred to the Laurentian system, is a 

 true igneous granite, as seen in its intrusion into the adjacent schists, in its inclusions 

 of masses and fragments of other rocks, and in its metamorphic action on limestone 

 in contact. 2. This granite is distinctly foliated, the gneissic structure being caused 

 by lateral pressure, * * * 3. The granite is intrusive in a thick group of quartz- 

 ites, quartz-schists, hornblendic, micaceous and talcose (?) schists, and crystalline 

 limestones, called the Kilmacrenan series. These rocks are truly crystalline, but 

 usually thin-bedded and fine-grained. 4. The crystalline schists are bounded on the 

 east by a semi-crystalline series, consisting of quartzose grits and itacolumites, quartz- 

 ites, crystalline limestones, compact dolomites, phyllites, interlaminations of grit and 

 schistose matter, and finely foliated micaceous schists." J 



These conclusions as to the irruptive origin of the gneiss are confirmed by 

 later observations of the same investigator on the Galway gneiss. § 



In the pre-Cambrian or Archean of Brittany, Barrois recognizes the irrup- 

 tive character of the gneisses which correspond to our Laurentian. He 



says — 



" Ces gneiss alternent avec des lits interstratifies de micaschistes et d'amphibolites, 

 et passent a des granites gneissiques qui les penetrant a la facon d'une roche eruptive. 

 L'ensemble des gneiss et micaschistes granitiques avec granites gneissiques rappelle par 

 ses caracteres lithologiques L'etage dimetien, propose par M. Hicks, dans le pays 

 de Galles, le gneiss fondamental d'Ecosse, certains gneiss laurentiens du Canada, 



*Geol. Survey of Canada, Summary Report for 1887 and 1888, 1889, p. -27a. 



t Ibid., p. 85a. 



{Quart. Jour. Geol. Soe., Vol. XLI, 1885, p. 239. 



I Quart. Jour. Geol. Soe., Vol. XLIII, 1887, p. 517. 



