GEOLOGY OF THE COAST DISTRICT. 63 1 



there. In Rollinsford the exposures lie to the south of the Portland 

 turnpike, appearing a short distance west of L. Stackpole's and along the 

 boundary road west of Fresh creek. In Dover there are a few outcrops 

 between Fresh creek and the main Cochecho river. The western limit 

 is at Sawyer's mills, and it is the prevailing rock west of Bellamy river 

 south of the Durham road. There is not much of the sienite in Mad- 

 bury, because of the narrowness of the town. Durham is chiefly under- 

 laid by this rock. It occupies ledges at the village, and at five places on 

 the direct road to Newmarket. West of the railroad it extends to school- 

 house No. 4. Following around the Great bay it is found to alternate 

 repeatedly with the Merrimack slate, as is the case all the way to Exeter 

 village. The slate is wider in the town of Newmarket than at any other 

 point between Dover and Exeter. The west border of the sienite is rep- 

 resented as even, perhaps through ignorance. All through Durham the 

 seams in the sienite dip north-westerly, as if they indicated the place of 

 strata. The more southern portion of this range displays a character- 

 istic feature of the exposures. They are very numerous, not much loose 

 material overspreads the ledges, and the soil is consequently barren. 

 There is also a profusion of boulders scattered upon the surface, whose 

 presence is usually a sure guide to the western limit of the area. 



In Brentwood the western limit is reached at Marshall's corner, and it 

 lies next to gneiss. Seeing sienite blocks at Brentwood post-office (Craw- 

 ley's falls) used for piers of a bridge, I inquired for their source, and was 

 told they came from a quarry about a quarter of a mile to the south. I 

 have put in a small area to represent this statement, not feeling confident 

 that it can connect with the main mass to the east. The unusual amount 

 of surface deposits in Kingston and East Kingston obscure the ledges 

 along the proper line of the continuation of the sienite, yet we have hints 

 of it in Hampstead and Atkinson, and better evidence in Salem. There 

 is reason to believe in its existence also farther south-west in Dracut. 



There may be a dioritic ledge on the east side of Exeter river, a mile 

 before coming to the north-east line ; but nearly all the east part of Exe- 

 ter is so covered by drift as to make a knowledge of the ledges impracti- 

 cable, save after a very thorough examination. The very point of the 

 town touches our fifth area of sienite, from Greenland to the south line 

 of Kensington. There are exposures of sienite along the Winnicut river. 



