THE r.UlLDlXc; OK AN ISLAND. 



2 I 



Central Slope, at Montpellier, Morning Star, Bonne Esperance, La Rcine and 

 Barren Spot, wc find all these layers sloping, not to the southwest, as we found 

 those of the opposite side, but to the southeast. We find this same dip also '^ 

 in the pieee of the marl formation across the valley and resting directh' against ^^ 

 the Salt River Hills namely, at the estates Windsor and Concordia. It is 

 also interesting to notice that the amounts of the dips of this new set are 

 about the same as those of the set previously examined. It appears, then, 

 that if wc could cut the beds of the Central Slope through from east to west 

 we should see them sloping inwards from the east and the west towards some 

 central line where they would meet, a line which geologists call a synclinal 

 axis, the whole arrangement of the rocks thus sloping together being called 

 a syttclinal. The case may be easily represented by partially- opening a book, 

 when the leaves to right and left will represent the sloping la\ers of rock, 

 forming the synclinal, and their junction down the middle will represent the 

 synclinal axis. If we further give the book a tilt from one end, calling it the 

 northern end. we shall get a still closer representation of the case before us, 

 for we have found that the rock layers do not dip in from due east and west, 

 but on both sides have an inclination also to the south. The diagram shows 

 how the limestone layers of the Central Slope rest on the older formation. It 

 will, of course, be understood that the black and white bands in no sense rep- 

 resent the layers. They merely indicate the slopes of the system. 



How TO Find the Synclinal Axis. 

 To tind where this synclinal axis runs is a task of no great difficulty, and 

 is of very great interest. The obvious plan to pursue is to cross the slope 

 along several lines going east and west, and to note on a map* the dip of the 

 rocks at every place where we can see it till we get, at all events, the approxi- 

 mate position of the line we are looking for. If we commence with the road 

 along the Princess plain, we find, at Belle Vue and the hills around, several 

 quarries and small road-cuttings, all of which show dips to southwest. At Big 

 Princess we find the same, then a southerly dip, and, at a cutting in a range 

 due south of St. John's residence, we find a dip to south-southwest ; but at 

 Montpellier and Morning Star, as well as on a road ascending the hills east of 

 the former place, we find that the dip is southeast. Hence wc see that the 

 synclinal line passes somewhere near the Estate St. John's. If we take the 

 road along the top of the hills ascending from Belle Vue we find a similar 

 condition ; the road-cuttings shew dips to the southwest until we approach the 

 turning where the road goes south to Rattan, and here the dip is southeast. 

 Along the roads which cross the Central Slope more to the south we find 

 southwest dips till we reach the neighbourhood of Diamond and Ruby; but a 

 short distance farther on we find at Barren Spot southeastern dips on the west 

 side of the village, and it is plain that we have crossed the synclinal axis. 



* The reader who may wish to follow up this investigation for himself should procure one of Captain 



Parsons' charts, or the chart of Santa Cruz, published by the Hydrographic Office, Washington, on which 

 to note his observations. 



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