200 R. A. Daly — Secondary Origin of Certain Granites. 



"The most prominent features of these gabbro masses are 

 those of dikes. As has already been mentioned, the larger one 

 [the one referred to in the present paper] in many places presents 

 perpendicular walls both to the north and to the south. It occu- 

 pies all the highest portions of the point, and these are in a 

 straight line. It has the appearance of an intrusive mass, and is 

 like any one of those forming the numerous points to the north 

 of the international boundary line. It has been regarded as a 

 dike by both Irving and 1ST. H. Winchell. Its contact with the 

 sedimentary rocks is only occasionally to be seen. At several of 

 these contacts the eruptive has the appearance of having escaped. 

 from between the dike walls and thrust itself for a short distance 

 between the fragmental beds, or having piled itself up around 



the dike orifice and overlapped the intruded rocks At only 



two places on the north shore do the fragmental rocks appear, 

 and at these places they are far below where they should be were 

 they interbedded with the gabbro, and in neither case is the con- 

 tact like that of interbedded eruptive and sedimentary rocks." 



He concludes that : 



" The larger mass of the Pigeon Point gabbro is in the form of 

 a dike, which has broken through its walls at certain places and 

 intruded itself between the strata of the surrounding rocks."* 



In accordance with his view Bayley's cross-sections show 

 vertical contacts among all the igneous rock members and also 

 between sediments and eruptives. 



On the other hand, Professor JST. H. "Winchell states, in a 

 personal letter to the writer : 



" All my observations bearing on the relations of the gabbro to 

 the Animikie on Pigeon Point lead to the conclusion that the 

 gabbro is later than the Animikie. But the term gabbro here is 

 made to include those coarse non-ophitic dikes that resemble gab- 

 bro and which are also allied to diabase. There are abundant 

 places where this rock is in the form of sills in the Animikie. 

 The great backbone of Pigeon Point, which is the most dis- 

 tinctly gabbroid of the intrusive rocks, is simply a large example 

 of a sill, while, as I interpret the structure, many of the dikes 

 cutting the Animikie are only contemporary offshoots from it." 



With Winchell's view there agrees the observation of Bayley 

 that the feldspar phenocrysts of the porphyritic gabbro are 

 sometimes " arranged in rude layers parallel to the dip sur- 

 faces of the quartzite. Their longer axes are usually in the 

 direction of the dip of the sedimentary rocks. "f This orienta- 

 tion suggests flow-structure parallel to contacts. Professor 

 Bayley has, by letter, restated to the writer his conclusion that 

 " the gabbro was intruded as a boss or huge dike, certainly not 



* Op. cit, pp. 22-23. f Op. cit., p. 23. 



