MOUNT GREYLOCK. 133 



what is above outlined, probably because <>t' the wide reach of territory 

 covered by the Taconic belt, and the overshadowing importance of the 

 stratigraphic relations on either side of it, as well as the imperfection of the 

 topographic maps hitherto published, and possibly because of the somewhat 

 rugged character of portions of the mountain. 



The raisons d'etre of this report are: That Mount Greylock, in itself, 

 offered one of the best fields for the study of the relations of the Taconic 

 rocks to each other, and that sections across it, when extended eastward, 

 northward, and southward, cut the underlying and older l-ocks where the 

 latter were being studied in detail by the same division of the U. S. Geo- 

 logical Survey; that careful work here would aid in unraveling the geology 

 farther west in eastern New York; that the geologic field work has been 

 based upon a more correct topographic map; that the observations made 

 have been very numerous (in all, 1,850), and have been carefully recorded 

 on such a map; that the work has been done in the light of recent advances 

 in orographic science, notably of the special investigations of Swiss and 

 Norwegian geologists into the structure of metamorphic rocks; that a large 

 collection of specimens has been gathered, illustrating principles of struc- 

 ture, from which large thin sections have been prepared for microscopic 

 study; that the photographic camera has been freely used in the field as 

 well as the study, and that the lithologic specimens gathered in the course 

 of this structural work have been subjected to optical examination by a 

 petrographer. Prof Pumpelly has also brought his wide experience and 

 critical judgment to bear upon the supervision of the entire work. 



PHYSIOGRAPHIC. 



The northern third of the western portion of Massachusetts is marked 

 by three main parallel mountain masses having the trend common to the 

 Appalachian system. The most westerly is the Taconic range, the crest of 

 which divides the states of New York and Massachusetts; the most easterly, 

 situate about ten miles east of the New York line, is Hoosac mountain, and 

 the central one is Mount Greylock. East mountain and Potter mountain 

 together constitute a fourth but subordinate mass, connecting the Greylock 

 mass with the Taconics farther south. 



Mount Greylock with its spurs forms a topographic unit It is sep- 



