458 



TraHSdcfio/if! 



Finally we shall consider the Pleistocene deposits. These are almost 

 entirely gravel deposits, the only exception being the fairly large formation 

 occurring to the west of the Waiau River and bordering Te Waewae Bay. 

 The formations are composed of beds of sand, clay, and shingle, with oc- 

 casional seams of lignite in the lower portions. These lignites are usually 

 poor ; occasionally well-preserved trunks of trees are found in them, and 

 a well-marked vegetable structure is often seen ; sometimes they contain 

 resin, like the coal in places at Nightcaps. 



The low land on the west of the Waiau is also composed largely of gravel, 

 and consists of a fairly flat plain, interrupted here and there by small hillocks, 

 which give to it an appearance very like that presented by a peneplain. 

 The valley of the Waiau River, too, in its upper portion is said to be strewn 

 with fragments of gneiss and greenstone, along with other eruptive rocks. 



The grave's all along the coast from the Waiau to Jacob's Estuary are 

 all referable to this period. They are usually, however, covered over by 

 silt and surface soil. Their origin is probably due to the spreading-out by 

 the sea of the detritus brought down by the rivers. 



Such, then, is the general geology of this district. The following sections, 

 together with the one previously given showing the relation of the Long- 

 wood to the geological structure of the south-west of Otago, vdW serve to 

 illustrate the main features just outlined : — 



Waimeamea coal 



(brown) Longwood Range 



NW 



Limestone 



Limcstor.e 



20 miles 

 Fig. ('>. — Skction from Jacob's Estuary to tiik Waiau River. 



h. Palaeozoic slates. &c. 



Fig. 7. 



c cL c e c J 



-From North of Mount Pleasant to the Sea-coast. 



a. Oainaru foi'inatioii. I). Basalt, c. Palaeozoic slates, d. Granite, e. Melaphyre. 



/. Gravel plain. 



It will be interesting, before conciuding, to compare the district with 

 that of the Coromandel Peninsula, in Auckland. One cannot but be struck 

 with the similarity on broad lines between the two. We have seen that the 

 Longwood district consists of a main central ridge running north and south, 

 with spurs given off on all sides, and the whole densely wooded. The main 

 axis, or what might be called the base, consists of Palaeozoic slates. These 

 are pierced, as we have seen, by dykes consisting of diorite, melaphyre, 

 and granite. On each side of the axis come younger rocks of Tertiary age. 



