624 STRATIGRAPHICAL GEOLOGY. 



parallel band, and near D. D. Whidden's in Ward No. i. There must be 

 many others. Near the south end of Newcastle the origin of these gran- 

 itic beds is apparent. They have been formed by the alteration of sand- 

 stones in situ. There is nothing indicating disturbance in these beds, 

 while there is a freshness about the mica crystals. None of the larger 

 beds are probably over 200 feet in breadth. 



Dr. Jackson examined the rocks about Portsmouth. A few sentences 

 are extracted from his report, stating the phenomena in his own language : 



The rocks to which I refer are the dark blue flinty slates, possessing an imperfectly 

 stratified structure, a very compact texture, sonorous when struck by the hammer, and 

 often breaking with a more or less distinctly conchoidal fracture. Occasionally they 

 evince a passage into an imperfect micaceous slate, especially where they border on 

 granitic rocks. * * Another change is also observed in the flinty slate rocks near 

 the railroad cutting in the vicinity of Portsmouth. The rock is filled with an infinity 

 of reticulated veins of carbonate of lime. This may have been produced by the fusion 

 [infiltration] of calcareous matter contained in the rock by the action of heat. * * 

 Iron pyrites abound in this locality. * * The strata of flinty slate are much con- 

 torted; and this contortion took place,. evidently, anterior to the eruption of the trap 

 dykes. The flinty slate contains numerous veins of compact feldspar, which probably 

 were formed at the epoch of the elevation of the granite rocks. * * The joints are 

 generally in directions parallel to those of a rhombic prism. * * The flinty slates 

 are succeeded by granites, which in numerous places have been erupted so as to isolate 

 portions of the slate by intrusion between their masses. Such phenomena would give 

 to a casual observer the idea that the slates and granite alternate with each other. It 

 will be found on further observation that such is not the case, for the primary rocks 

 have merely been forced in between portions of the slate. Near the house of Samuel 

 Langdon, a mile and a half from Portsmouth on the road to Boar's Head, a mass of 

 granite has been intruded through the slate, and occupies a considerable area, beyond 

 which the flinty slate again appears, and then gives way to a regular granite and gneiss 

 formation, which extends through a large portion of Rye. In Portsmouth the intrusion 

 of granite veins and trap dykes into the flinty slate may be seen in Shoar's woods. 



The Isles of Shoals have been neglected. I have noted the fact of the 

 presence of gneiss on Star island, without stating which is the predomi- 

 nant dip. The following brief notes about them are taken from Jackson. 

 Star island is said to be composed of a coarse variety of granite, having 

 large crystals of white feldspar, gray quartz, and but little mica, with 

 intercalated beds of mica schist. Along the middle of the island is a 

 trap dyke running north-east. There is very little soil upon the island. 



