CONSTITUTION OF THE KNOB 



339 



dolomite just beneath. The question of the source of the inclusions be- 

 comes of importance in the discussion of another problem and will be 

 reverted to presently. 



The knob is surrounded by black shales, chiefly Nbrmanskill, and it 

 would seem as if the lava must have risen through a large thickness of 

 such shale lying above the limestone. There are also frequent bands of 

 very resistant grit in these shales. Under the circumstances the utter 

 lack of recognizable inclusions from this formation in the knob is most 

 astonishing. There are some larger masses of shale involved with the 

 lava, but they can hardly be regarded as inclusions. There may be some 

 content of comminuted shale in the lava, the evidence for or against this 

 not being decisive. 



Structural Features: Shear Zones 



The dissection of the knob by quarrying operations has brought to light 

 some structural features which were not discernible before. Woodworth 

 found evidence of interrelations of lava and shale which suggested fault- 

 ing of the knob to him, and the opening of the knob has brought to light 

 much more evidence of the same sort, and evidence of severe compressive 

 disturbance and dislocation exists all through the lava mass. A few 

 sketches and a comparison of them with the photograph of the knob 

 (plate 10) will assist in the exposition of the observed relations. 



Figure 1.— Shale overlying Lava on low Point projecting from Stark* Knob 



houso° Wi Thii\h^ Ph ° t0graph ** * he base of ^ knob just to the right of the boiler- 

 house ihis shale wedges out into the lava of the knob; in other words, shows lava 

 both above and below it. It is not a contact between lava and overlying shale but I 

 shale wedge within the lava mass. * 8 ' l a 



Figure 1 is a sketch of the relations shown in a low point which pro- 

 jects out to the east from the base of the knob, and which has remained 

 anquarried because of the shale overlying the lava, so that there is no 

 great thickness of the latter above ground. A short distance to the south 

 oi this point, hack of the boiler-house, is another similar one in which the 

 rock relations are just reversed, lava overlying shale. In this latter case 



