176 



DB. C. T. TEECHMAIsN OIH 



[vol. Ixxiii, 



Mount Potts. 



The chief interest of this locality centres in the plant-beds 

 discovered by McKay in 1877. Great uncertainty has arisen over 

 the age of these beds and the associated marine fossils, owing 

 to Hector's determination of Glossojytej-is among the flora. The 

 district, which is extremely mountainous, was described by McKay,^ 

 who states that the plant-beds of Tank GruUy underlie the marine 

 * Sjyirifer ' Beds. Later, how^ever, he says that plant-remains 

 overlie the Kaihiku in the district between the Eangitata and 

 Ashburton Rivers.- The fossils in the marine beds have been 

 variously determined as Permian, Lower Carboniferous, or Upper 

 Devonian ; but my examination of the Geological Survey Collection 

 and of a series collected by Prof. Marshall convinced me that they 

 "are all Triassic. They occur in black, compressed and fractured, 

 slaty argillites. The following forms are present: — 



A Nautilid. 



Small g-asteropods with angular 



wliorls. 

 Baonella indica Bittner. 

 Pinna sp. 

 Aiiodontophora sp. 

 Spirigera liailiikuana, sp. nov. 



Spiriferina (Cyrtina ?) carolinas, 



sp. nov. 

 Spiriferina sp. 

 Halorella sp. 

 Dielasma sp. 

 Mentzeliopsis sp. 

 Crin Old- stems. 



Mr. McKay told me that 3fi/tilus prohlemaficus occurs there, 

 but there is no trace of Monotis or Fseiidomonotis. 



The great majorit}^ of the fossils are those of the Kaihiku and 

 are of early Upper or late Middle Trias. The only forms that 

 indicate a Carnic horizon are Nautilus and Pinna. Reptilian 

 remains occur in some of the beds, the large narrow amphicoelous 

 vertebra? of which suggest some form of Ichthyosaurus. 



The late Dr. E. A. N. Arber ^ examined a series of the plants 

 which Mr. D, G. Lillie collected here in 1911, with the result that 

 the supposed Glosso2yteris turned out to be a new^ form, to which 

 he gave the generic name Lingiiifolium, and the whole flora proved 

 to be either late Triassic, Rhaetic, or early Jurassic. Dr. Arber, 

 however, informed me that, at present, it is impossible to distinguish 

 between late Triassic and earl}^ Jurassic floras. From the evidence, 

 both of the flora and of the associated marine fauna, it seems per- 

 fectly justifiable to attribute an Upper Triassic age to the plant- 

 beds of Mount Potts ; but the question as to the position of the 

 plant-beds relatively to the marine horizon is one on which further 

 evidence is needed. 



Mount St. Mary. 



The fossiliferous outcrop at Mount St. Mary occurs at an 

 altitude of 5160 feet. Fossils occur in three zones in a thickness 

 of 50 feet: the two low^r zones are slaty shales and the upper a 



' Bibliography, 28, p. 92. 

 ^ Bibliography, 2. 



Bibliography, 28, p. 95. 



