Fairbanks.] 



Geology of Point Sal. 



39 



forced its way up through the shales, tilting them nearly vertical on 

 the lower side. In the center is a mass of metamorphosed shale 

 sharply folded in a syncline and dividing the outcrop into two parts. 

 On the upper side the shales rise in a gentle swell from a nearly 

 horizontal position, and are exposed in an abrupt wall 3 feet high 

 resting directly on the intrusive body (Fig. 2). The metamorphism 

 is not noticeable for a distance of more than 30 or 40 feet, but in 

 the first 8 feet it is very strongly pronounced, the soft shales being 



Figure 2. — Basaltic intrusion in the Knoxville. 



changed to a compact flinty rock. The shales inclosed in the center 

 have apparently only a slight depth, and everything points to the 

 fact that the magma never reached the surface, but has been exposed 

 by erosion in comparatively recent times. The manner in which 

 the strata have been lifted reminds one very strongly of a lacolite, 

 but the relation of the eruptive to the strata below is in all probabil- 

 ity not of that character. 



Microscopic Character. — The slides prepared for the microscope 

 show a fairly uniform groundmass, in which porphyritic crystals of 

 feldspar and pyroxene occasionally appear. The pyroxene occurs 

 4 



