284 



It is, typically, a stiff loamy clay, which makes a good brick earth, but varies, in 

 places, sometimes taking the form of a light loam, and, at others, a marly loam, 

 or passes into sand and gravel. These Recent alluvia often occur overlying the 

 mottled beds and can be distinguished from the latter by their uniform coloura- 

 tion (sometimes greenish), less compact form, and often by a plane of erosion; 

 the reddish clays not infrequently fill in gutters that have been excavated by 

 stream action in the older mottled clays, as can be seen in the cliffs at Ardrossan 

 (Howchin, W., 1918b) and also on the eastern side of the Gulf, references 

 to which will be given later. 



These Recent clays can be studied in the cliffs near Seacliff and Marino, 

 where a washout, caused by a small runner, has developed within recent years 

 a considerable canyon which extends from the beach almost to the railway line. 



Both the mottled clays and the newer reddish clay show horizontal and 

 truncated bedding at a considerable height above the present sea level, giving evi- 

 dence that they were laid down, either before the present valley of Gulf St. Vincent 

 was invaded by the sea, or at a time when the sea margin was more remote than 

 it is at present. 



Nodular Travertine. — This is a concretionary and chemically formed lime- 

 stone which is a common surface feature throughout the district where the 

 subsoil is calcareous. In the lower portions of the bed it is a marly clay, 

 becoming more nodular and limy in its upper portion, and often forms a 

 limestone crust, or sheet, near the surface. It is well developed at the Cove, 

 varying in thickness from 6 feet to 15 feet. At the north end of the Cove, at 

 the back of the principal ice-polished face, it makes a scarp and is very nodular 

 in structure. 



SUB-SECTION B. 

 BLACK POINT TO ROCKY POINT (3| MILES). 



Black Point, as already described, forms the northern headland to the broken 

 coastline that goes under the name of Hallett's Cove. The Point consists of 

 very dark-coloured purple slates, of Cambrian age, so that, when seen from the 

 seaward it has a very black and forbidding aspect, which has given rise to its 

 name. The prominence which the rocks make at this point affords an excellent 

 cross section of the beds, showing an acute anticlinal fold that is fractured and 

 slipped on the axial plane. 



Hallett's Cove, as a whole, forms one of the most picturesque spots on the 

 coast within the limits of Gulf St. Vincent. It is scarcely a Cove in the ordinary 

 acceptation of the term, as there is no sheltered area of sea space and only a 

 slight indentation on the coastline. The Field River, which finds its outlet at 

 the Cove, is only a creek that can easily be stepped across, and has no inlet 

 from the sea, except at very high tides. The Cove is a natural amphitheatre of 

 broken ground, bounded by rocky headlands. It owes its existence not to 

 marine erosion, but to the effects of rain beating on the exposed faces of soft 

 rocks and the transporting agencies of small runners that excavate channels in 

 the soft material. 



Cambrian Rocks in Section B. 



There is no outcrop of Cambrian rocks within the amphitheatre of Hallett's 

 Cove itself. A large mass of purple rock, 12 feet in length, exposed near the 

 head of the amphitheatre was, at first, thought to be an inlier of the older rocks, 

 but by the removal of the soft material by subsequent erosion it was seen to be 

 an erratic in the till, and is now fallen apart in two pieces. The Cove is, how- 

 ever, bounded by Cambrian slates and quartzites on the landward side. Good 

 sections are exposed in the creek that reaches the sea a little to the northward 

 of Black Point, and also in the Field River, near the southern extremity of the 

 Cove, as well as in a small creek a little to the northward of Field River. 



