76 



soft, arenaceous, yellow clay, changing to sandrock of variable 

 dimensions, viz., from nine to twenty feet. From it have been 

 taken specimens of Terebratula and other molluscs, all totally 

 different from those of the Grits. It is succeeded by a whitish, 

 plastic, sandy clay, or clayey sand, abruptly separated from the 

 preceding by a seam of hard arenaceous limestone only one 

 inch thick. This bed contains numerous small fossils, Fibularia 

 gregata (Tate), small Pectens, &c, and overlies a yellow clay, 

 containing abundant specimens of Ostrea, Avicula, Pecten, 

 JEcJiinoderms, &c, and even some teeth of fishes have been 

 obtained. It seems a remarkable fact that the fossils in 

 these lower layers should have preserved the original structure 

 of their shells, though very brittle ; while those in the upper 

 grits have been changed into silicates, or dissolved away. 



At Muloowurtie Point the {last-mentioned clay rests directly 

 and uncoirformably upon the crystalline limestone called " Ar- 

 drossan marble" (C, fig. 2) in undulating curves, and several 

 of the upper members of the series thin out and disappear 

 gradually. The total aggregate thickness of the whole series 

 of the lower clays may be estimated at not much exceeding 

 40 feet, where observed. As to what age these lower clays belong, 

 the following remarks may not be out of place : — Some speci- 

 mens of the "Turritella Grits" having been submitted to Pro- 

 fessor Tate, P.G-.S., President of this Society, I was favoured 

 by him with the information that he identifies their charac- 

 teristic fossil with that of a member of the lowest f ossiliferous 

 series at Aldinga, the oldest Tertiary strata hitherto known in 

 South Australia, and belonging to the Eocene period ; there- 

 fore, as none of the fossils hitherto discovered in the lower 

 clays at all resemble those of the grits, and embedded in a 

 lower stratum, these clays may ultimately prove to be of still 

 greater age. 



Lower Silurian. 

 At the elevated parts near Ardrossan the local Tertiaries 

 overlie unconformably, as stated above, a firm, felspathie 

 sandstone and grit, designated " Ardrossan Sandstone" (B, 

 figs. 2 and 3) . This sandstone is sub-crystalline in texture, fine 

 grained in the upper, and coarse in the lower portions, and of 

 greyish white colour, and occasionally coarse and even con-, 

 glomerate. The upper portions show false bedding distinctly, 

 and separate into large blocks, while the lower present a dis- 

 tinct cleavage at nearly right angles to the plane of deposition. 

 It is quarried on Section 77 (see fig. 1) for building stone, for 

 which it is well adapted. The measurements taken there gave 

 the following angles, viz. : — Dip, 15 degrees easterly (average), 

 and strike N. 63 degrees E. The same rock also forms escarp- 

 ments on the seaward faces* of the hills in Sections 33, 31, &c, 



