I So STRATIGRAPHICAL GEOLOGY. 



together by a granitic paste ; and oftentimes in the midst of the north- 

 westerly trend there are ledges and smaller masses retaining the northerly 

 course. It is easy to say that some portions of the original strike were 

 retained, even after the exertion of the disturbing agency, altering the 

 position of the principal portion of the areas in order to explain these 

 phenomena. Second, cases have been cited showing that fragments of 

 the slates occur imbedded in the underlying granites. This is most 

 easily explained by saying that pieces of the slates were broken off during 

 the disturbances connected with the eruption of the granite, and caught 

 in the fluid mass. If so, of necessity the granite came into being later 

 than the slate. 



In a part of my labor in the Notch I had the pleasure of the company 

 of Professor Dana, who made many valuable suggestions and queries. 

 After communicating to him some facts observed after his departure, he 

 writes : " There can now be no reasonable doubt, I think, with regard to 

 that Notch valley being the course of an anticlinal, the veins and the 

 broken line of rock being so extensive. [See p. 167.] The stopping 

 short of the andalusite slate [on Mts. Willey and Tom] is strange. The 

 point of special importance in connection with it is, what rock appears to 

 be its continuation } Is it the porphyritic [spotted] granite that lies to 

 the west of it ? Is it a stop-off through a fault, or through a change in 

 the material of the stratum, leading to the development of a different 

 crystalline rock by metamorphism.?" 



The distribution of the slates will be alluded to again further on, after 

 describing the other areas of this formation among the mountains. 



T/ie NotcJi valley bctivcen Willey brook and Bcniis. Our observations 

 in the valley between the andalusite slates on Willey brook and the reap- 

 pearance of the Montalban gneisses at Bemis, are fewer than their imiaor- 

 tance demands. The first ledge of the Conway granite, 2000 feet below 

 the Willey brook, is mentioned on page 175. It is finer grained than 

 usual, and useful for building purposes. None of the spotted variety of 

 granite shows itself adjacent to the slates on their south side, as in the 

 case farther north. This Conway granite seems to conform to the posi- 

 tion of the slates underlying them. Opposite the Willey house this rock 

 is coarser, and closely agrees with its most common type of mineral 

 structure. Passing up Willey mountain it is displayed in many high 



