2O 



GENERAL GEOLOGY 



dikes of various basic igneous rocks. In places it has 

 picked up large fragments of the limestone that occurs in 

 mass near at hand. It has contorted and twisted the bed- 

 ding very much, and has formed contact minerals (esso- 

 nite, pyroxene) in the limestone at the border. 



On the nunatak at the eastern front of Hugh Miller 

 Glacier the tonalite is cut by a diorite dike which contains 

 a great horse of the tonalite and is itself cut and shifted 

 by a later aplite dike (fig. 4). 



FIG. 4. DIKES IN GLACIER BAY. 



The limestone is determined as Carboniferous by Pro- 

 fessor H. S. Williams, on the evidence of a single speci- 

 men of Lonsdalia, and the tonalite must be younger, as it 

 penetrates and alters this. It resembles closely the tonalite 

 of Plover Bay, Siberia, and St. Lawrence Island, de- 

 scribed below; and on St. Lawrence Island similar lime- 

 stones and contact deposits are also found. 



The only point where observations were made which 

 added to the information contained in Reid and Cushing's 

 map 1 was at the small glacier discharging into Reid Inlet 

 next west of the Hugh Miller Glacier and named by the 

 party Reid Glacier. This glacier was visited by Messrs. 

 Gilbert and Palache, and the rocks on either side of its 

 front were studied. 



The point on the east side is made up of coarsely crys- 

 talline white marble, which is cut by a network of igneous 

 dikes (plate n). 



1 i6th Ann. Rept. U. S. Geol. Survey, part i, plate xc. 1896. 



