THE BUILDING OF AN ISLAND. 



103 



NOTES. 



On Finding the Anticlinal Axis of the Northwest. 



It has been noted (page 45) that an anticlinal 

 axis divides the rocks of the Northwestern Hills 

 which dip to the south or thereabout from the rocks 

 that dip to east-northeast or thereabout, and that 

 such axis is found to lie about west-northwest and 

 east-southeast. 



In order to be able to lay down this line we 

 must traverse the roads passing through the hills 

 and note the dip of the stratified rocks wherever 

 we can find them. 



In this examination it will be advisable to com- 

 mence with the road passing from the estate Little 

 La Grange, in the valley, to the estate Puneh on 

 the top of the hill. 



The diagram shows the sequence of the differ- 

 ent dips met with along this road. The measure- 

 ments between the successive points are not exact, 

 having merely been stepped out ; but they may be 

 of some use to a reader who may care to follow up 

 the observations. It may, in the first place, be 

 noted that near Punch the southerly dips that have 

 been met with during the ascent change over to 

 northeast. Next we may note that at several 

 points the strata are vertical or nearly so, while 

 at other points they pass over to northerly dips. 

 This need not confuse us, for we have already 

 learned that rocks, which on the whole dip to the 

 south, may in some places be vertical and in others 

 be even pushed over so as to get a reversed dip. 

 The great value of the observation in this case is 

 that it enables us, when we pass to the seashore, 

 to see that we may properly retain small areas of 

 northerly dip in the large area of southerly dips, 

 seeing in the rocks of such smaller areas examples 

 of reversion of dip on a considerable scale, and 

 not change from one larger area to another. 



Following the coast from Frederiksted north- 

 wards we first come to the cliff at Spratt Hall, 

 where we find slaty rocks in regular layers dipping 

 to north at about 50. This is so great an amount 

 of reversion that we might be inclined to think 

 that we must have come to the north slope of the 

 anticlinal if we did not observe that the dip lacks 

 the more marked easterly tendency which we find 

 farther on when we actually come to the great 

 northeast slope of the anticlinal. At Butler's Bay, 

 farther north along the shore, we find a like dip 

 as to direction ; but the rocks have not been thrust 

 so far over, the dip being 75 degrees to north-by- 

 east. Continuing northward, we come to the real 

 change when we arrive at the estate Northside, 

 where we find in a cutting a dip of from 30 to 40 

 degrees to east-by-north. Our having now passed 

 into the area of the northeast dips is confirmed 

 when we come into Ham's Bay, where we meet 





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