GEOLOGY OF THE COAST DISTRICT. 625 



Hog island is composed mostly of mica schist. Duck island shows gran- 

 ite and gneiss. The other islands arc granitic. 



The most modern-looking rocks I have seen are situated in a cut by 

 Brackett's station on the Portsmouth railroad. Geologists familiar with 

 Cambrian fossiliferous strata would find many ledges in the east part of 

 Rockingham county very similar to those yielding trilobites, worms, and 

 mollusca elsewhere. Careful search will undoubtedly develop them here- 

 after. 



Kittery, York, and Eliot, Maine, are a continuation of these slaty 

 quartzites of the Merrimack group, and they follow up the Newichwan- 

 nock river between the two sienite areas to Berwick. Similar strata may 

 be followed along the coast nearly to Portland. On the Kennebunk and 

 Saco rivers are areas more argillaceous, possessing a north-west strike. 

 This fact suggests the existence of later groups resting uncomformably 

 upon the Merrimack series, similar to the Cambrian along Parker river, 

 Massachusetts. 



Great bay must be underlaid by these rocks, as they yield to decom- 

 position sooner than the hard sienite. One would naturally expect to 

 find a shallow synclinal beneath the water of Great bay, but the strata dip 

 at large angles, though showing the basin form. From Exeter village to 

 South Berwick the slates occupy only a small space adjacent to the water, 

 being a fringe skirting the sienite. What irregularities of position be- 

 tween these rocks have been perceived, are represented upon the map. 

 These may, perhaps, have arisen from igneous ejections, accompanied 

 with lateral pressure. A like irregular boundary may be seen in York, 

 Wells, and farther along the coast of Maine. 



Plate XXV illustrates the relations of the Merrimack group to the adjoining forma- 

 tions. Fig. 106 shows the order of rocks between Pawtuckaway pond and Exeter vil- 

 lage. At the west end in Nottingham are the north-westerly dipping mica schists, 

 carrying the quartz band. Then appears the most important anticlinal, dividing the 

 group naturally into two parts, followed by unimportant flexures and the Epping syn- 

 clinal. The sienite of Exeter occupies an important place at the east end of the sec- 

 tion, seemingly supporting the slates ; and the high westerly-dipping schists at the east 

 side of the village would seem to indicate an inverted anticlinal, when compared with 

 those on the other side of the sienite. 



Fig. 107 gives an insight into the relations of the strata between Brentwood and Sea- 

 brook. In the first-named town there is an area of gneiss adjacent to the sienite. 

 VOL. II. 79 



