REPORT ON THE GEOLOGY OF ESSEX COUNTY, 

 MASSACHUSETTS, TO ACCOMPANY MAP. 



BY JOHN H. SEARS. 



(Curcttor of Mineralogy and Geology, Peabody Academy of Science. 1894.) 



A complete account of the geology of even so small an 

 area as that of Essex County could only be given after de- 

 voting the time of a long life to the work in the iield and 

 laboratory. I do not, therefore, pretend to offer this re- 

 port as a completed account, but rather as the results of 

 several years' continuous devotion to the study of our 

 rocks ; rocks of such a complex character that in many 

 cases their satisfactory determination seems almost hope- 

 less. 



In justice to those who have previously investigated the 

 rocks of the county, and to assist future workers in this 

 field, a listof books andpapers which have come to my no- 

 tice, treating more or less fully of the subject, is appended. 

 In making this list I have been greatly aided by the notes 

 of Dr. M. E. Wadsworth on the Mineralogy and Petrog- 

 raphy of Boston and Vicinity, published in the Proceed- 

 ings of the Boston Society of Natural History, vol. xix, p. 

 217, 1877. Nearly all that has been published, however, 

 is of a general character, very little being given in detail. 



With the exception of the centennial map of the geolo- 

 gy of Massachusetts published in the Proceedings of the 



(118) 



