274 W. S. Bayley — Soda- Granite, etc., of Pigeon Point. 



and a few subordinate constituents. The second variety resem- 

 bles quartz-porphyry. Well terminated quartz crystals and 

 occasional brick-red and greenish white feldspars are scattered 

 through a very fine grained, dark red or purple groundmass, 

 whose major portion consists of a granophyric intergrowth of 

 quartz and red feldspar. Both rocks exhibit in such a marked 

 degree the features of igneous rocks that it was concluded, 

 mainly on the evidence of their structure, that they were 

 original eruptives, i. e., that they both solidified from a mol- 

 ten magma which was derived from some place within or 

 beneath the earth's crust. In the article referred to it was 

 stated that " All the field relations seem to point to the original 

 character of the rocks. Thev occur in dikes and veins inter- 

 secting other rocks, and the contact between them and the 

 quartzites which they cut is sometimes clearly seen. It must 

 be confessed, however, that without microscopical and chemical 

 evidence of the identity of these rocks with the quartz por- 

 phyry [of the Lake Superior region] their true nature would 

 be difficult to discover from the field relations alone. A more 

 careful examination of the structure of the point, will probably 

 reveal facts which will place beyond doubt the conclusions 

 reached by the microscopical examination." 



Since the above was written a second visit to Pigeon Point 

 has been made, but contrary to expectation the relations of the 

 red rgck to the gabbro and the quartzites, with both of which 

 it is in contact, appear to contradict the above statements 

 rather than to affirm them. 



As indicated in a previous article* the rocks on the point 

 comprise evenly bedded slates and quartzites, a large mass of 

 olivine-gabbro, trap dikes cutting the gabbro and the bedded 

 rocks, and a red granitic and porphyritic rock. The latter 

 occur in large quantity only between the gabbro and a series of 

 contact rocks, which have evidently resulted from the slates 

 and quartzites by alteration. (See map, fig. 1.) The granular 

 rock passes by imperceptible gradations on the one hand into 

 the gabbro, and on the other into the quartzites. Prom the 

 larger masses of the red rock dikes and veins extend into the 

 members of the contact belt. In a few places large bodies of 

 the same rock have been forced under the unaltered fragmen- 

 tals and have thrown them into gentle folds. The red rock is 

 found in largest quantity where the contact belt is widest, and 

 is absent from those places in which there are no indications 

 of a metamorphic action in the slates and quartzites. 



On the other hand, there are several places on the point 

 where the gabbro and the quartzites are separated by two or 

 more members of the contact belt without the interposition of 



* This Jourual, May, 1888, p. 388. 



