45 



The Geology about Port Wakefield. 

 By Peofessor E. Tate, F.a.S., &c. 



[Bead July 4, 1881.] 

 Plate IV. 



Haviug critically inspected tlie rock specimens obtained 

 from the Port Wakefield bore, and having geologically ex- 

 amined the country in its vicinity, I venture to submit tho 

 subjoined notes on the correlation of the strata passed through 

 in the sinking, and a geological section, generalising the strati- 

 graphical phenomena, as a supplement to Mr. E-utt's account 

 of the Port AVakefield sinking — one of the deepest which has 

 yet been attained in this colony. 



The site of the bore is on the south-east edge of an extensive 

 salt marsh, having a general level of about 16 feet above lovp^- 

 water mark at Port AYakefield. Profusely strewn over the 

 surface of the marsh are the common species of shells of our 

 existing mud-flats, such as Am^uUarina Quoyana, Risella tceniata, 

 Tellina deltoidalls, &c. More decidedly marine species occur 

 abundantly at lower depths, even in the shallow excavations 

 made for drainage purposes. Above the edge of this elevated 

 marine bed there is, at about one-quartei* oi" a mile to the east 

 of Port Wakefield, a fine example of an old beach, excavated 

 to some six and eight feet in depth for ballast, which is highly 

 charged with Area trapezia, the valves often in apposition. 

 Similar "Recent Marine Deposits " occur at various points on 

 our shore line. (See Trans. Phil. Soc, II., p. Ixviii. et seq^.j 

 114.) 



From the level of the salt marsh, there extends landward a 

 gently inclined plain composed of red loam, which gives place 

 to gravels, more or less angular, at the upper limit of the 

 formation, at about 250 to 300 feet, where they abut against 

 the flanks of scarped hilly ground. These beds, as seen at the 

 surface, are identical with those constituting the Adelaide 

 Plain, and to which I have applied the term " Pliocene Drift. '^ 



The rocks of the hilly ground of the Hummocks Eange, as 

 exposed in the line of railway between the South Hummocks 

 and Kulpara Stations, are composed of mudstones, quartzites, 

 and felspathic sandstones, the former chiefly constituting the 

 main mass of the middle part of the series. They have a dip of 

 about 40°, bearing a little south of true east. 



The strata passed through in the Port Wakefield sinking I 

 refer to : — 



