CHAPTER VIII, 



GEOLOGY OF THE COAST DISTRICT. 



KPhE Coast district embraces the south-east corner of the state, prin- 

 JC cipally Strafford and Rockingham, and a little of Belknap counties. 

 It lies altogether east of the Merrimack hydrographic basin, and includes 

 most of the Salmon Falls drainage area, save a little treated of in the 

 preceding chapter for convenience. It is the least elevated part of the 

 state. On a natural scale, where the horizontal and vertical are the 

 same, and the size that of our general map, the highest point in Rock- 

 ingham county would be elevated one sixteenth, and the most conspicu- 

 ous hill in the whole district, in Gilmanton, would rise only one eighth 

 of an inch above the base level. The general average would not exceed 

 one twenty-fifth of an inch. The great erosions that have brought the 

 region to this lowly condition have removed the crests of the folds to an 

 unusual extent; and the ice has been instrumental in covering large 

 tracts with sand, gravel, and till, thus preventing the solution of many 

 important stratigraphical problems. The surface deposits, as represented 

 by colors upon the map, cover more area in this district than in any of 

 the others. While this prevents so full a knowledge of the solid rocks, 

 it enables us to carry on successfully the study of surface geology, as 

 will appear in the sequel. 



The following formations crop out in the Coast district, including the 

 adjacent portion of York county. Me., and a little of Essex county, Mass., 

 so far as represented upon the south-east part of the map: i. Porphyritic 



