HTNGHAM. 



INTRODUCTION. 



The town of Hingham, Mass., forms the south shore of 

 Boston Harbor for three miles, from Weymouth Back River 

 across Hingliam Harbor to Weir River Bay ; and extends 

 inhand from six to seven miles, crossing the present border of 

 the Boston Basin, i. e., the southern limit of the sedimentary 

 and volcanic rocks. The town is thus divided into two distinct 

 and very unequal geological areas ; and, as the general map 

 (PI. 1) shows very clearly, the dividing line is quite irregular. 

 The sedimentary rocks and the interbedded lavas arc limited 

 almost wholly to the northwest coi'ner of the town, extending 

 but little south of the railroad and having only a slight areal 

 development east of the harbor. While over the remainder of 

 the town, embi'acing more than five sixths of the total area, 

 the numerous lodges comprise only granitic rocks (granite, 

 diorite, and felsite), and intersecting dikes of diabase. 



The granitic area of Hingham is essentially similar to, as 

 well as continuous with, that of Cohasset and Nantasket on the 

 east and A\'^eymouth and Braintree on the west, the entire 

 South Shore district being a unit in this respect. But, as was 

 pointed out on page 2, the sedimentary and volcanic rocks 

 borderinf^j the fijranite on the north and forminfj the immediate 

 shore of the harbor are fjir less uniform in character and struc- 

 ture, and by their diversity fully warrant or necessitate the 

 division of the South Shore into several distinct areas, which 

 are best described separately. These geological areas agree 

 approximately with the political divisions, the geology of North 



