STRUCTURE OF THE MOUNT WASHINGTON MASS. 733 



mountain mass. Proceeding northward, one of the 

 minor synclinals in the western limb of the anticlinorium 

 increases in depth and width by a northerly pitch of 

 its trough line, so as to show at the surface, first, the 

 Egremont Limestone, and then more and more of the 

 Everett Schist. The eastern limb of the anticlinal has, 

 in consequence, been narrowed, then compressed and 

 overturned, until east of Mt. Race its axis 1 inclines 

 westward about 35 degrees. The northerly pitch of 

 its crest line carries it continually deeper, until finally 

 it disappears beneath the limestone on the east flank 

 of Mt. Race (cf. Fig. 1). By this process the anti- 

 clinorium of the southern portion has been developed 

 in the central portion into a compound fold consisting 

 of two deeply corrugated synclinals (eastern and 

 western schist ridges) and a central corrugated antici- 

 lina, which brings the limestone to the surface in the 

 central plain. Proceeding northward still, the flexures 

 sharpen and deepen and become reversed, much as 

 Professor Dana has described. This narrowing of the 

 folds contracts the mountain at its north end, and the 

 succeeding southerly pitching crest and trough lines 

 bring the limestone higher and higher until the over- 

 lying schist disappears altogether. To facilitate the 

 comparison of the flexures, Fig. 4 is introduced, the 

 curves being those of the contact of the Egremont 

 Limestone and the Everett Schist as developed in the 

 series of sections. The map, as well as the sections, 

 show that the small schist ridges in the limestone near 

 Salisbury are mainly infolded Riga Schist with the 

 axes of the folds inclined eastward. 



Variable Thickness of the Egremont Limestone. — 

 The upper limestone of Mt. Washington forms the 



1 In this paper the term " axis " is used for the axial-plane bisecting 

 a flexure, and never for the crest line or trough line. Cf. Margerie et 

 Heim, Les dislocations de 1' ecorce terrestre. Zurich, 1888, p. 53. 



