732 A TREATISE ON METAMORPHISM. 



amount of work required for the liquefaction of a great mass of solidified 

 rock. Work must be done in fusing the material, and work must be done 

 in expanding the material. Besides raising the temperature to the fusion 

 point, all the latent heat of fusion must be supplied. The heat required 

 for the process of fusion of rocks in a furnace is very great. Ordinarily a 

 magma has a temperature only slightly in excess of that required to hold 

 it in the liquid form. Therefore, that it could furnish a sufficient amount 

 of heat to liquefy immense masses of solid rocks seems highly improbable. 

 And it has already been seen that it can not be assumed that the necessary 

 heat is furnished by orogenic movements, although this may be a helpful 

 factor. 



While fusion of solidified rocks of the lithosphere on a great scale, 

 either by magma or by orogenic movement, or the two combined, is to be 

 proved, it is certain that fusion has locally occurred. One of the clearest 

 instances of fusion or semifusion in America is that on Pigeon Point, 

 described by Bayley." At this place is a metarhyolite, called keratophyre, 

 on one side of which is a great mass of gabbro, and on the other side of 

 which are the slates and quartzites of the Animikie series. The keratophyre 

 has all the characteristics of an eruptive rock young-er than the gabbro. 

 In a position between the keratophyre and the gabbro is a coarse-grained 

 red rock, which is intermediate in character between the two and grades 

 into each of them. It is therefore regarded as a product formed by the 

 intermingling of the gabbro and rhyolite magmas, the gabbro having been 

 actually fused for a short distance from the keratophyre. For a distance 

 of about 9.5 kilometers, with a few interruptions, the contact rock has a 

 width of from 30 to 90 meters, and for one continuous stretch of nearly 

 3 kilometers it has an averag*e width of fully 60 meters. If this rock, 

 which is intermediate in composition between the metarhyolite and the 

 gabbro, and which grades into each, and yet has the textures and struc- 

 tures of an igneous rock,' really represents the result of the action of the 

 quartzdieratophyre on the gabbro, as it appears to do, it is one of the best 

 known cases of actual fusion of one rock by another. 



Between the metarhyolite and the slates and quartzites of the Animikie 

 there is another contact belt which extends for about the same length as the 



"Bay ley, W. S., The eruptive and sedimentary rocks on Pigeon Point, Minnesota, and their 

 contact phenomena: Bull. U. S. Geol. Survey No. 109, 1893, pp. 1-121. 



