222 



MR. JUKES-I5R0WNE AND PROF. HARKISON 



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irrep:ular ridges which have a 

 jreneral oast and west direction. 

 In this area there are no deep 

 watercourses or gullies like 

 those Avhich traverse the central 

 j)art of the island, and all the 

 water falling on it is carried off 

 by subterranean channels. 



It is separated from the 

 central part of the island by a 

 low flat plain, which nowhere 

 rises to more than 150 feet 

 above the sea. On the north 

 side of this the ground rises by 

 a series of terraces to about 

 350 feet, above which there is 

 a steep slope rising in a short 

 distance to 500 feet. The 

 width of this low ground be- 

 tween the two contour-lines of 

 300 feet is rather less than 

 two miles in the narrowest 

 part, but it broadens gradually 

 both eastward and westward. 



From the above description, 

 it is clear that when the sea- 

 level coincided with the contour 

 of 300 feet the Christchurch 

 E-idge formed a separate island, 

 divided from the mainland by 

 a navigable channel with an 

 average width of two miles and 

 a depth of over 25 fathoms. At 

 a still earlier period in the 

 uprise of the area it must have 

 presented the appearance of a 

 small barrier-like reef between 

 three and four miles long by 

 five or six furlongs in width. 



At the east end of the ridge 

 and at a level of about 200 feet 

 there is a small exposure of 

 lladiolarian earth, from which 

 it would seem that the coral- 

 rock of the ridge rests on these 

 deposits. On the other hand, 

 the rock which forms the low 

 ground to the north appears to 

 rest on Scotland beds ; for in 

 the well at Dodds estate on 

 the farther slope, clay was 

 found directly below the coral. 



