394 Transactions. — Geology. 



Eoad Cutting, Thomas River," collected by Mr. McKay in 1874. 

 Mr. Enys, however, assures me that he has never seen this 

 species from here, but that he gave a specimen, which he had 

 collected at Pareora, to Mr. McKay, distinctly telUng him at the 

 time where it came from ; and it is possible that iu this way 

 the species may have got into the list. 



The map accompanying this paper is reduced from the 

 topographical survey made by Mr. Adams in 1882, which 

 Mr. Enys supplied me with. It is, of course, more accurate 

 than the one Dr. Hector had in 1872. The geology will, 

 I trust, be found correct in the mam ; but that portion 

 bounded by the Porter River, the West Coast Road, and the 

 fault south of the Thomas River is purely hypothetical, the 

 rocks here being covered by a thick deposit of gravel, which 

 is not cut through by any stream. I was also called back to 

 Christchurch suddenly, before I could examine the inliers of the 

 upper limestone lying on the western edge of the basin between 

 Thomas River and Coleridge Creek, and without having suffi- 

 ciently examined the eastern slopes of Castle Hill and Flock 

 Hill. 



General, Geological Structure. 



The physical features of this basin have been sufficiently 

 described by Mr. McKay. It is a rock-basin, hollowed out of a 

 massif of sandstones, mudstones, and greywaekes belonging to 

 the Maitai System. The rocks filling the basin are divided into 

 three distinct formations, as follows, each resting unconform- 

 ably on the rocks below it : — 



3. Pareora System (Lower Miocene of the survey). — 

 A series of blue clays, shales, and sandstones, 

 sometimes unconsolidated, with a total thickness of 

 000 or 700 feet. 



2. Oamaru System (Upper Eocene of the survey). — 

 Coralline limestone, underlain by volcanic grits and 

 tuffs, passing iu the soutli into thick scoria beds. 

 Thickness of sedimentary rocks, 150 feet. 



1. Waipara System (Cretaceo-tertiary of the survey). — 

 Argillaceous limestone and calcareous sandstone 

 underlain by marl, below which are green and other 

 coloured sandstones. Maximum thickness about 

 1,200 or 1,300 feet. 



Speaking roughly, the rocks may be said to dip everywhere 

 towards the centre of the basin ; but as the basin is much 

 longer than broad, they form a syncline whicli runs from the 

 upper part of Coleridge Creek in a N.N.E. direction, west of 

 Castle Hill, to Parapet Rock (where the Pareora System stops) 



