PKEFACE . Vll 



To Dr. T. S terry Hunt I am indebted for much valuable 

 instruction, advice, and criticism, while a student in the Mas- 

 sachusetts Institute of Technology and since, without which the 

 performance of this work by me would have been impossible. 

 Though placed in a position most favorable to a thorough 

 acquaintance with Dr. Hunt's views concerning the origin 

 of crystalline rocks and their relations to the more recent, 

 fossiliferous rocks, I entered the field with a general disbelief 

 in their applicability to the rocks of this region, which my first 

 observations only strengthened ; and any conclusions in har- 

 mony with these views which may be found in this paper have 

 been reached in opposition to preconceived ideas wholly at 

 variance with them. 



For valuable data, freely contributed, my acknowledgments 

 are also due to Mr. L. S. Burbank, of Woburn ; Mr. T. T. 

 Bouve, President of the Boston Society of Natural History; 

 Mr. F. W. Very, of Hyde Park; Prof. W. H. Mies, of the 

 Massachusetts Institute of Technology ; Mr. W. W. Dodge, 

 of Cambridge, and others. 



The chemical analyses recorded in this paper were made in 

 the Woman's Laboratory of the Massachusetts Institute of 

 Technology, and for these I am under special obligations to 

 Mrs. Alice B. Crosby, Mrs. Ellen H. Richards, Miss E. M. 

 Walton, Miss H. A. Walker, and Miss Jennie M. Arms. 



The President and Directors of the Eastern Railroad Com- 

 pany have assisted very materially in the exploration of Essex 

 County by granting free passes over their line. 



Boston, August, 1878. 



