BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 7, pp. 349-362, PL. 16 MARCH 14, 1896 



DISINTEGRATION AND DECOMPOSITION OF DIABASE AT 

 MEDFORD, MASSACHUSETTS 



BY GEORGE P. MERRILL 



(Presented before the Society December 26, 1895^ 



CONTENTS 



Page 



Introduction 349 



Description of locality 349 



Petrographic features of the rock ..... 350 



Earlier references to the disintegration 350 



Present aspect of the dike 351 



Mechanical analysis of disintegrated rock 351 



Chemical analyses and their discussion 352 



Time limit and extent of disintegration 358 



Relative rapidity of rock-weathering in high and low latitudes 359 



Introduction. 



In the paper herewith presented the writer has endeavored to illustrate 

 the chemical and physical changes taking place in the breaking down of 

 rock masses through the ordinary conditions of atmospheric action com- 

 monly grouped under the name of weathering. The general tendency 

 of the investigations has been the same as those pursued in the case of 

 the disintegrated granitic rocks of the District of Columbia, the results of 

 which were presented to the Geological Society of America at its meeting 

 in Baltimore one year ago.* 



Description of Locality. 



The rock selected for investigation in the present instance is a coarsely 

 crystalline, somewhat granular diabase, which occurs in the form of a 

 large dike exposed almost continuously from the Mystic river, in Med- 

 ford, Massachusetts, northward toward Spot pond, for nearly two miles. 



* Bull. Geol. Soc. Am., voi. 6, March, 1895, pp. 321-332. 

 XL— Bull. Geol. Soc. Am.; Vol. 7, 1895. (349) 



