64 



induced by the contact. Crossing the south boundary into 

 Muloowurtie, we find them forming both sides of Eogues* 

 Gully to a height of about 200 feet, thence extending south- 

 ward they are finally determined by a wide granitic dyke 

 between Trooka Creek and Pine Point. About Muloowurtie 

 Point they are found at and below sea level, underlying the 

 older Tertiaries. The boundaries assigned to the Silurian on 

 the map are, of course, only proximate, the rock being seldom 

 exposed to any extent. 



Detached smaller areas in the form of hills occur in the 

 northern portion of Cunningham (Sections 172, 182, 181, 173, 

 160, 161, 150, and 151) at a greater distance from the sea, and 

 somewhat differing in aspect (but not in the form of deposit) 

 from the marbles. It is more saccharoid in structure, contains 

 small irregular hollows, and is crossed by short disjointed 

 cracks frequently lined by a dark film ; possibly the hollows 

 mentioned may be the only remaining indications of organic 

 inclosures, at first contorted by metamorphic changes and 

 finally removed through chemical agencies. Specimens of an 

 exceedingly similar rock (if not identical) were sent to me 

 from Kilkerran, where they were obtained in a well about 

 ninety feet deep. If they be Silurian, this would indicate that 

 the whole width of the Peninsula partook of the depression. 



The marbles, as well as the last-mentioned limestone, are 

 accompanied occasionally by concretions of magnesite. The 

 felspathic rock forming the uppermost stratum of the Silurian 

 series assumes — according to situation — either the structure of 

 a conglomerate or a gritty sandstone, but most frequently the 

 former. The most northern locality observed directly by me is in 

 a quarry in Section 77, near Ardrossan, whence it extends south- 

 ward, overlying the marbles, and traceable at several places 

 around the Silurian area landward. The same rock appears 

 also on the western incline of the Yorke A^alley Hills, where its 

 stratification can be studied in a quarry situate in Section 214, 

 Hundred of Maitland. Xear Ardrossan the dip is easterly ; 

 at Yorke Valley Avesterly, with about the same low angle and 

 gentle foliation as the limestones. Though now very hard and 

 tough, they were obviously deposited in a shallow, turbulent 

 sea as a gravel or sand, exhibiting in many parts, like the 

 modern sands of a beach, unmistakable false bedding, denoting 

 that the land experienced a rapid elevation during [their 

 deposition, as no gradation from the fine-grained limestones to 

 the conglomerates has been noticed. In some localities, or in 

 some layers only (generally the uppermost) the constituent 

 grains are fine and evenly bedded ; in others they are more or 

 less coarse, sometimes CA^en verging upon true breccias in 

 anjrularitv, denoting: that the material had been derived from 



