\\\ s. BayUy — Soda-Granite, etc., qf Pigeon Point. 275 



anv of the red rock. At the falls ^\' Pigeon River, on the 



north side o\' the point at its extreme western end. a large mass 

 of gabbro has cut through slates and qnartzites and has altered 

 them in a manner somewhat analogous to the alteration of 



similar rocks bv granite and other plutonic rocks. 



Av other place-, notably OH the north side o\' the point, the 



gabbro and fragmental rock.- are in contact without the least 

 trace of anv alteration in the latter. 



From the relations of the gabbro, the red rock and the con- 

 tact belt, it is plain that either the gabbro or the red rock is the 

 cause of the contact belt. If the latter, the red rock is a true 

 irruptive; if the former the red rock is either an irruptive 

 between the metamorphosing agent and the products of its 

 action, or is itself one of these products. 



It is the object of the present note to point out the reasons 

 that lead the writer to the conclusion that the red rock is of 

 contact origin, that it has been produced by the action of the 

 gabbro upon the slates and qnartzites. At first glance it would 

 appear' that the evidence is strongly in favor of the red rock 

 a- the cause of contact phenomena. This view is apparently 

 favored bv the fact that the gabbro has produced no very great 

 alteration in the surrounding sedimentary beds in those local- 

 ities where no traces of the occurrence of the red rock can be 

 found. It has not affected the bedded rocks on the north 

 side of the point, nor are immense dikes of a similar rock 

 known to have produced any change in the slates and quartzites 

 at other points along the north shore of Lake Superior. If, 

 however, we examine these facts critically it will be found that 

 they do not exclude the possibility of a secondary origin for 

 the red rock, or of the active agency of the Pigeon Point 

 gabbro in promoting the metamorphism of the elastic beds. 



The existence of the keratophyre in dikes and veins in the 

 contiguous slates and quartzites show conclusively that it once 

 existed in a plastic condition. Its structure indicates that it 

 once existed as a molten magma, or in such other condition as 

 would allow of its complete crystallization, unless we assume 

 with Wadsworth* and Juddf that the porphyritic and grano- 

 phyric structures may arise from* secondary causes. The im- 

 pregnation of the contact rocks by the material of the red 

 rock is further evidence that this was once in a liquid state. 



If we assume the original molten or liquid condition of the 

 red rock, as it seems we are perfectly justified in doing, all of 

 its present characteristics are explained, whether it be regarded 

 as an extraneous igneous rock or whether it be considered as a 

 final product of contact action. In either case its most charac- 



*Geol. and Nat, Hist. Surv. of Minn., Bull. No. 2, pp. 12 and 68. 

 \ Quart. Jour. Geol. Soc, May, 1889, pp. 175-178. 



