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idea of a general Natural History Survey was for the first 

 time definitely announced and provided for in its plan of 

 organization. The Geology fell to my share, and since 

 iny acceptance of a position in the Massachusetts Insti- 

 tute of Technology, I have, with the assistance of the 

 fourth year's class of Mining Engineers from that Institu- 

 tion, been able to continue the work. 



The first fruit of this labor is exhibited here to-night 

 in a map of Marblehead Neck. The ground- work of the 

 whole is a copy of the Plane Table sheet of the United 

 States Coast Survey, which has been given to me espec- 

 ially for this work through the kindness of Prof. Pierce. 

 The wonderful accuracy of this map is shown by the test 

 to which these investigations have subjected it. The 

 copy before you has been enlarged three times, and is on 

 a scale of .3000 or about eighteen inches to the mile. 

 Notwithstanding this enlargement I have been able to 

 identify every small indentation in the coast-line, and the 

 outline of every projection ; as a topographical map for 

 the foundation of a geological survey it is perfect. 



The principal intention has been to map out in detail 

 the actual outcrojjjPof rock which project above the sur- 

 face. These are painted in solid colors. Dark bluish 

 purple shows the porphyry, which occupies the upper 

 two-thirds of the neck and a strip on the harbor-side, 

 reaching to the east end of Devereux beach ; dark drab 

 mica-schists and fine-grained gneiss, which fill out the 

 southeastern portion ; while patches of vermilion scat- 

 tered over both indicate the presence of an eruptive 

 granite. 



The precise outline of each outcropping or exposed 

 rock was not attempted, but the general direction of the 

 longest axis of each mass is given, and such an approxi- 

 mation to the precise outlines as could be obtained by a 



