BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 24, PP. 335-350, PLS. 10-11 JUNE 16, 1913 



NORTHUMBERLAND VOLCANIC PLUG 1 



BY H. P. CUSHING 



(Read before the Society December 28, 1912) 



CONTENTS 



Page 



Location « 335 



Historical 335 



Description 336 



Constitution of the knob 337 



General character of the constituent material 337 



Inclusions 337 



The section 337 



Structural features : shear zones 339 



Microscopic character 342 



Chemical composition . 344 



Is the lava in place? 346 



The inclusions 348 



Age of the igneous rock 349 



Location 



A knob of volcanic or effusive rock of quite exceptional occurrence and 

 character is found in Saratoga County, New York. It stands close to the 

 west bank of the Hudson River, one mile north of the village of Schwy- 

 lerville and 10 miles east of Saratoga Springs. Seen from the east, it 

 appears as a knob some 70 feet in height on the margin of the terrace 

 which fronts the river. Viewed from the west, it is much less prominent, 

 standing only about 30 feet above the general level of the terrace. The 

 terrace steadily rises in level to the west and soon exceeds the altitude of 

 the knob's summit. 



Historical 



The knob is located well to one side of ordinary routes of travel and 

 wholly escaped the attention of geologists until discovered, studied, and 

 described by Woodworth in 1901. a Tt subsequently remained un visited 



1 Manuscript received by the Secretary of the Society, April 21, L918, 



2 21st Kept. New York State Geology, pp. rl7-24. 



(335 



