392 Transactions. — Geology. 



within easy access of Blind Bay, where a steamer calls regu- 

 larly ; and a good carriage road might easily be formed. As 

 they now are, visitors can without difficulty go there, and to 

 those who have not yet done so, I say, by all means go. 



To the botanist and geologist I venture to promise an 

 excellent field; and to the lover of nature abundance of material 

 will be found, enough at any rate to prove the mighty workings 

 of a strong but unseen hand. 



Art. LII. — On the Geology of the Trelissick or Broken River Basin, 



Selwyn County. 



By Prof. F. W. Hutton, F.G.S. 



[Read before the Philosophical Institute of Canterbury, 3rd June, 1886.] 



Plates XXIV. and XXV. 



Introduction. 



The Trelissick Basin lies among the mountains which separate 

 the Piiver Rakaia from the Waimakariri, and it drains into the 

 latter. The West Coast Road from Christchurcli to Hokitika, 

 on leaving the Canterbury Plains, does not follow up the valley 

 of the Waimakariri, but ascends to Porter's Pass (3,097 feet), 

 between the Thirteen-mile Bush Range and Mount Torlesse ; 

 then descending, and passing through the Trelissick Basin, it 

 reaches the Waimakariri at an elevation of 1,808 feet above the 

 sea. The road then ascends once more to Arthur's Pass (8,013 

 feet), which lies on the watershed between the east and west 

 coasts. The ascent to Porter's Pass is rendered necessary by 

 the deep, narrow, and almost impassable gorge, six miles in 

 length, by which the Waimakariri reaches the plains (PI. XXV., 

 fig. 1). In this respect the Waimakariri differs from the Rakaia 

 and Rangitata, further to the south, which enter the plains by 

 broad shingle valleys. In the sequel, 1 will offer an explanation 

 of this remarkable peculiivrity. 



The first notice that I can find of the gcolog^^ of the district is 

 in the " Catalogue of the Colonial Museum," (Wellington, 1870,) 

 in which the fossils collected by J. D. Enys, Esq., are arranged 

 in t\YO groups — one in the middle tertiary or Cucullfea beds, the 

 other in the lower tertiary or Ototara series. The fossils, 

 however, had got rather mixed, and in 1872 Dr. Hector visited 

 and mapped the district, dividing the rocks into three forma- 

 tions, which he called Lower Miocene, Upper Eocene, and 

 Cretaceo-tortiary. The fossils in the Wellington Museum, 

 coming almost entirely from the two upper of these formations, 



