114 Prof. J. D. Dana — Metamotyhism of 



which often characterizes ejections that have come up from regions 

 beneath the supercrust.' Sediments, and therefore sedimentary 

 deposits, are liable to frequent and sudden changes as to material, 

 which igneous outflows cannot imitate. Secondly, the rocks are likely 

 to have no columnar (basaltic) structure ; because the fractures to be 

 filled in such cases are fractures in rocks which are participating in 

 the movement, and which, therefore, are heated rocks, and not cold. 



Again, the phenomena of contact and the facts as to inclusions, 

 structure and superpositions, may have distinctive peculiarities. 



C. The condition of fusion or plasticity in the Cortland region. — 

 To answer the question before us we have, therefore, to consider 

 more closely than has been done the phenomena of contact of the 

 schistose with the massive rocks over the Cortland region, the 

 peculiarities of some of the inclusions, the characteristics of some of 

 the so-called veins or dykes, and the characters of the rocks as to 

 their transitions, structure, and relative positions. 



3. Special Facts from the Cortland Begion. 



a. Contact-phenomena betioeen the schistose and massive rocJcs ; 

 fads connected ivith the inclusions ; stratigraphical relations to the 

 limestones. — The facts with reference to inclusions and all contact- 

 phenomena bear directl3'^, as will appear, upon the question as to 

 any stratigraphical relation in the Cortland rocks to the limestones ; 

 and they are, therefore, here taken from the vicinity of particular 

 limestone areas. 



(1) The vicinity of Cruger's limestone area. — The small lime- 

 stone area near Cruger's (see map) lies mostly to the south and 

 east of the station ; only a small portion about forty feet in 

 greatest width borders the river west of it, beyond the first brick- 

 yard (/), the rest of the westward extension of the limestone 

 being beneath the river. The schistose rocks directly and con- 

 formably adjoin it on the north, the average strike of both being 

 N. 70° E, and the dip 75° to the northward. In the south-eastern 

 portion of the area there is a twist in the whole to the north-west. 

 The limestone is finely crystalline granular, mostly white in colour, 

 and over the hills to the eastward contains crystals of white pyroxene. 



The schist north of the limestone has a thickness of about a 

 thousand feet. Toward the limestone, it is a silvery mica-schist 

 containing a little black mica and an abundance of very small 

 garnets. A hundred yards or so to the north it is staurolitic, 

 the staurolite occurring in grains of a clear chestnut-brown colour 

 and rarely in distinct crystals ; and it also in some parts becomes 

 quartzose and consequently^ thick-bedded. There are, besides, 

 seams containing much magnetite ; and at one place an intercalation 

 of a black micaceous rock containing some felspar which is about 

 equally orthoclase and a soda-lime species. After another hundred 

 to a hundred and fifty yards northward, in the course of which it 

 becomes increasingly staurolitic and garnetiferous, and passes in 



1 The term mpercrusl is used for that part of the earth's crust which has heen 

 made by sedimentation, the true crust being restricted to the part beneath wliich is a 

 result simply of cooling. 



