48 



THE BUILDING OF AN ISLAND. 



But the two sets of strata do not dip away at right angles to the axis but 

 in a sloping direction on each side (Fig. 20), and we must ask, how is this to 

 be explained ? For an explanation we may fall back on an earlier result of our 

 investigations. In our study of the limestone formation we saw that some of 

 the lines marking the divisions between sets of limestone strata having differ- 

 ent dips ran across other lines, indicating that the forces of elevation acted in 

 two directions, crossing each other, though perhaps not exactly at right angles. 

 We saw, for instance, that the limestones of the great Synclinal of the Central 

 Slope do not dip at right angles to the axis but come down to it from the 

 northeast on one side and from the northwest on the other, indicating a cross- 

 elevation from the north. 



Fig. 20. 



And, what has a more tlirect bearing on the case before us, we saw in" re- 

 gard to the anticlinal of the Mt, Eagle Ridge that as we followed the axis 

 from the ridge across the plain and down the Barren Spot Valley the strata on . 

 either hand passed away to southeast on the one side and to south-by-west on 

 the other, not by any means at right angles to the axis, but with a southerly 

 inclination which could onlv be explained bv supposing that there was also a 

 tilting from the north. So in the larger case we are now considering, we have 

 onlv to suppose that besides the pressure from the north-northeast which 

 pushed up the ancient strata into a great fold (or into folds, as we shall see 

 later), there has been another force acting from a line of elevation to the west 

 which has given the sloping direction of the dips on both sides of the anti- 

 clinal. 



When studying the Mt. Eagle anticlinal, the fust which we met with in 

 our investigations, we found that the case was well represented by an open 

 book turned down on the table and then tilted from one end. and the same 

 illustration will serve us in the present case. In fact, it seems that the illus- 

 tration of the open book, simple as it is, gives the whole story so far as the 

 directions of the dips over the areas in question are concerned, but it does not 



