Speight. — The Tertiary BeiU of the Trelissick Basin. 343 



E. VOLCANIC ROCKS. 



The volcanic rocks of the area have been described by Hutton. They 

 consist almost entirely of fragmentary matter, which is very thick between 

 Coleridge Creek and Whitewater Creek; in the latter this reaches 1,000ft. 

 approximately. The beds are also strongly developed near the mouth of 

 the Thomas and in Home Creek. The fragments are usually of small size, 

 pieces over 3 in. in diameter being rare, and are extremely well bedded, 

 indicating submarine deposition, from their association with limestones, 

 and from the marked amount of calcareous material which they frequently 

 show, and from the numerous marine fossil remains which they contain. 

 The fragments are of glassy character, at times with the yellow colour 

 characteristic of palagonite ; at others the glass is clouded with iron-ore 

 and with microlites of feldspar, and somewhat frequent crystals of olivine. 

 Deposits of the same character occur just outside the Trelissick Basin near 

 the junction of the Esk River with the Waimakariri, and near the junction 

 of Sloven's Creek with Broken River. In both these cases the beds are 

 well stratified and associated with beds of calcareous material, pointing to 

 a wide extension of the sea over the region in which the volcanoes were 

 situated . 



Hutton has noted the occurrence of dykes round the base of Prebble 

 Hill. They do not, however, appear to radiate from any particular point, 

 and are perhaps only remotely connected with the volcanic outbursts. 

 Similar dykes occur on the northern flanks of Mount Torlesse, somewhat 

 distant from the centres of explosive action, the most noteworthy 

 being that on the northern side of the bridge across Broken River, and 

 in Iron Creek, on the western boundary of the Mount Torlesse coal-mining 

 lease. 



Other intrusions have not been found in position, but numerous boulders 

 and pebbles of olivine gabbro are fovmd in the bed of the Porter River. 

 In all probability they have been shed from minor intrusions such as are 

 known to occur in the greywackes farther south in the Acheron Valley, 

 from which the large masses foimd in the gravels of the Rakaia River may 

 probably be traced. 



F. PALAEONTOLOGY. 



Although the correlation of the beds in different parts of the area can 

 be determined with reasonable certainty from their stratigraphical relations 

 alone, the palaeontological evidence on which their correlation with beds 

 outside the particular area is based must be considered in detail. The 

 fossil-content of the various beds will be dealt with in order, the authority 

 for the collection of the specimens being given in each case. 



The oldest bed in the area which has yielded plant fossils up to the 

 present is the plant-fossil bed in Murderer's Creek, the collection from which 

 was submitted to von Ettingshausen,* of Vienna. There is apparently some 

 doubt about the localities, but these were revised by Hector. In the list 

 given there the following species are recorded : — 



Quercus lonchitoicles Ett. Dryandra camptoniaefolia Ett. 



Planera australis Ett. Cassia pseudophaseolites Ett. 



* C. von Ettingshausen, Contributions to the Knowledge of the Fossil Flora of 

 New Zealand, Trans. N.Z. Inst., vol. 23, 1891, p. 250. 



