46 History of Hingham. 



much at the several localities. In attempting to obtain this, it 

 may be well to admonish the reader, if not a geologist, that in the 

 case of slates and some other rock's, the true lines of deposition 

 by no means correspond with the lines of cleavage. It is owing 

 to the planes of the latter that the rock is serviceable for the 

 uses to which it is put in the arts, as a roofing material, and 

 for other purposes. This kind of cleavage is called Slaty 

 Cleavage, and it is unquestionably due to great lateral pressure 

 of the material of which slates are composed, after its deposition. 

 The fact of such pressure being exerted upon the strata beneath 

 the surface is well-known, and experiments by Sedgwick, Tyndall, 

 and Daubree, upon clay and other substances, demonstrated that 

 the effect of pressure was to produce lamination. 



The writer has thought it well, before closing his remarks upon 

 the rock exposures of the town, to suggest two excursions that 

 may be made to advantage by students interested in them. One 

 of these is through the northern portion of Hersey Street, from 

 South Street to Elm Street. The rocks mentioned rest immedi- 

 ately on or quite near the margin of the road, and may be seen 

 without going any distance from it in the adjoining fields. Since 

 the examination has been made there has been some change on 

 the east side of the street by the erection of a building, and the 

 covering over of a portion of the rocks near ; but thus far none 

 that will lessen interest in inspecting those yet undisturbed. The 

 other excursion suggested is that of a visit to Rocky Xeck and a 

 walk along its shores, as promising more pleasure and instruction 

 than can be found in any other locality. 



Hersey Street. 



This street, in its northern part, affords a good opportunity to 

 observe a succession of the sedimentary rocks of Hingham with 

 the intrusive trap which is found with them. In ascending the 

 rising ground from South Street, there occurs, on the right side, 

 about 240 feet from the commencement of the road and back from 

 it, an exposure of Conglomerate. It shows itself quite near the 

 house of Mr. Allen A. Lincoln. Its face is parallel with the side 

 of the house and at right angles with the road. On the next 

 estate, 60 feet beyond, there is rock exposure near and facing the 

 street, the first part of which is composed of trap and constitutes 

 a dike six or more feet in width. This is succeeded bv conglom- 

 erate, with which it makes a close junction. This conglomerate 

 extends about 15 feet and is followed by a reddish slate extend- 

 ing 20 feet, in the centre of which is a second trap dike. Suc- 

 ceeding the slate is more conglomerate, which shows itself 50 

 feet or more. There is no further exposure on the right side of 

 the road for 1090 feet, and then it is found that the limit of the 



