H". \. Bayley — Soda-G-ranits^ <i<-.< qf Pigeon Point. 279 



the red rock is present, taken together with the fact that con- 

 tact rocks arc found in positions where they cannot have been 



produced by the action of the keratophvre, seems to point to 

 this conclusion as the mosl probable one. 



Prom the evidence at hand it would appear that the red 



rock is a product of contact action between the gabbro and the 

 bedded rocks, rather than an independent irruptive that has 

 altered the slates and quartzites. No conclusive evidence bear- 

 ing upon the question is available, but if the assumption of the 



sondary origin of the red rock is made, all the tacts observed 

 with reference to the distribution of the rocks on the point are 

 readily explained ; not a single one but i> in accord with this sup- 

 position. On the other hand, if the red rock is assumed as the 

 metamorphosing agent, there remain to be explained the contact 

 phenomena around the gabbro in those places where the red 

 rock is absent, and the peculiar distribution of this rock. The 

 view that the gabbro is the cause of the alteration of the slates 

 and quartzites, and the red rock is an independent irruptive 

 between the former and the latter, meets with the same objec- 

 tion as does the supposition that the red rock is the cause of 

 the contact belt. The presence of the red rock only between 

 the gabbro and the contact rocks, and in great quantity only 

 when the contact phenomena in the adjacent quartzite evince 

 intense action, is a mode of distribution for an independent 

 irruptive rock, which, to say the least, is peculiar. Since, 

 therefore, objections can be raised to any view that regards the 

 keratophyre as an original irruptive, and since, on the other 

 hand, every fact observed, either with reference to the gabbro 

 or to the red rock, accords with the assumption that the latter 

 is a product of contact action, and none can be found that con- 

 tradict this supposition, it would seem gratuitous to regard the 

 red rock as having originated in any way but by the fusion 

 by the gabbro of the fragmental rocks that lie upon one side 

 of it. The latter are slates and quartzites, many of which are 

 highly feldspathic. Chemical analyses of these show them to 

 have a composition not very different from that of the red rock 

 itself. 



It is hardly necessary to refer to the important bearing of 

 the above conclusion upon the discussion of the origin of 

 igneous rocks. The general view with regard to these is that 

 they have reached the surface from some permanent or tem- 

 porary reservoir of molten material below the earth's crust. 

 On the other hand, many geologists hold to the belief that some 

 of the igneous rocks have resulted by the metamorphism of 

 sedimentary beds Granite for instance is regarded as a meta- 

 morphosed sandstone. The only basis upon which this con- 

 clusion rests is the supposed gradation of gneiss into granite. 



Am. Jour. Sci.— Third Series, Vol. XXXIX, No. 232.— April, 1890. 

 19 



