Morgan. — Geology of the Patea District. 59 



Mr. W. Gibson, of the Geological Survey, visited Patea in September, 

 1914, with the object of reporting on the ironsand deposits of the district. 

 His report (6) describes only the beach and dune-sands. 



In 1917 Dr. J. A. Thomson published a paper (7) on the " Hawera 

 Series." in which he makes reference to the geology of Patea. The 

 Hawera series, he states, is well exposed in the cliffs between Wanganui 

 and Hawera. The mudstone or claystone (papa) forming the lower part 

 of the sea -cliff at Hawera is " probably about the same age as the Patea 

 blue clays, which are placed by Park below the Ostrea ingens bed 

 of Waitotara. It is certainly older than Castlecliffian, and is probably 

 Waitotaran.'" 



The observations lately published by Marshall and Murdooh (10) on the 

 fossils collected by them at Wanganui, Kai-iwi, Nukumaru, Waipipi, &c, 

 have an important bearing on the age of the Patea blue clays. 



Last October the writer paid a brief visit to Patea, and made observa- 

 tions which are embodied in the following pages. 



Physiographic Features. 



The district surrounding Patea forms part of that decidedly complex 

 feature generally termed the Wanganui coastal plain, which, viewed broadly, 

 may be said to extend along the south-west coast of the North Island from 

 Paraparaumu in south Wellington to Opunake in Taranaki. and inland to 

 the slopes of Mount Euapehu, while if Mount Egmont and the adjoining 

 volcanic ranges were removed the whole of Taranaki might be included in 

 the plain. The inland portion of the area just defined is for the most part 

 maturely dissected, and exhibits numerous irregular ridges of approximately 

 equal height in adjoining localities, separated by deep, narrow valleys. 

 The coastal belt, in marked contrast to the inland region, as a rule has a 

 nearly flat surface, sloping uniformly and gently towards the sea, where 

 it is usually, at least from Wanganui north-westwards, ended by dune- 

 capped cliffs of considerable height. Inland of Hawera there are one or 

 two well-marked marine terraces (" raised beaches "). 



The principal streams north of the Manawatu Eiver have cut deep, 

 rather narrow, steep-sided valleys in the soft rocks of the coastal area, one 

 result of which is that the railway from Wellington to New Plymouth has 

 to descend into and ascend our of each valley by a more or less steep grade. 

 Tk< j inland hills, as a rule, do not descend gently to the nearly flat coastal 

 belt, but rise with some abruptness from its inner margin. Thus the surface 

 of the coastal belt and the plane joining the tops of the inland hills and 

 ridges are distinctly unconformable. Hence the Wanganui coastal plain 

 (sensu lato) really consists of an ancient well-dissected coastal plain bordered 

 on its seaward side by a younger less-dissected coastal plain. 



The physiography of the area immediately surrounding Patea does not 

 differ from that of other parts of the coastal belt between Wanganui and 

 Hawera. The gently sloping coastal plain, as elsewhere, ends in dune- 

 capped cliffs, here about 100 ft. high. The Patea River flows at grade 

 through the plain in a deep relatively narrow valley with cliffed sides. 

 A mile from the sea the river is slightly entrenched in the valley-bottom, 

 so that the small flats on either side are above ordinary flood-level. This 

 seems to indicate recent slight elevation of the land ; but, as there also 

 seems to have been a slight depression in recent times, as shown by a 

 submerged forest at the mouth of the Waitotara Eiver. another explanation 



