276 Transactions. — Geology. 



From Colonial Laboratory Reports, Wellington, 1879-81, 

 [Mr. W. Skey, Analyst.) 



A, B, and C. — From section at M ; but C from a lower level 

 than A and B. 



You will please observe the differences in the analyses of A 

 and ]J, and C, with regard to the percentages of silica in each. 

 Now at the section marked L in diagram the percentage of silica 

 is about 50. In the lowest part of the chalk exposed at M the 

 percentage is 32-10, decreasing in the upper part of the bed to 

 15-69. 



The dip, as shown in accompanying diagram, is towards the 

 south-east — -that is, towards M. Now, taking all these facts 

 into consideration — the presence of P. williamsoni in both ; the 

 decrease of silica as we ascend in the chalk at M., and the dip 

 of the bed, there can, I think, be no reasonable doubt but that 

 the marl at L and the chalk at M are one and the same bed, 

 the marl being the lower and the chalk the upper deposit. 



At the time of the deposition of the bed, Mount Oxford 

 (1,392 feet high), distant about five miles, must have existed as 

 an island, whence disintegrated rock would be borne to the sea. 

 The high percentage of silica in the lower beds points to com- 

 paratively shallow water. Gradually the coast sank ; less and 

 less silica was deposited among the chalk ; and, finally, the 

 water became pure enough to admit of the growth of a coral reef, 

 teeming with Foraminifera. 



13 ut the elevatory agencies reassert themselves ; the coast 

 rises. Volcanic disturbance follows long ages of tranquillity : 

 basaltic lava streams How, where formerly the quiet lagoon 

 existed ; but although they may have obliterated the beauty of 

 the scene at the time, yet to them we owe the preservation of 

 this exceedingly interesting record of a portion of the past 

 history of our island. 



* Specimens collected by Mr. John Ingram, Lab. Nos. 2597 aud 2819. 



