26 



On account of this protected position the tidal currents 

 are very weak and are scarcely noticeable within the limits 

 of the bay, while the fluctuations of the sea are largely 

 controlled by the direction and force of the wind, the rise 

 and fall of the sea at any time being limited to a few inches. 

 These conditions are very favourable for the development of 

 a littoral fauna, among which Serpulae make a prominent 

 feature, forming a kind of miniature fringing reef, composed 

 chiefly of the calcareous tubes of these annelids, with a 

 tendency to assume circular outlines. 



Professor Pirsson offers no explanation as to the reason 

 why the serpuline growths on the Bermudas coast take a 

 circular form of growth, but, so far as the Encounter Bay 

 examples are concerned, I think an explanation is possible. 



The Permo-carboniferous till, which forms the cliffs and 

 marine platform at Encounter Bay, consists chiefly of an 

 argillaceous sand-rock that is easily acted upon by the sea, 

 and yet is sufficiently coherent to form a definite floor. It 

 extends inland throughout the Inman and Hindmarsh Valleys, 

 across the Bald Hills watershed to the shores of Gulf St. 

 Vincent, yielding, in many places, excellent sections. Within 

 the body of this argillo-arenaceous till, in many places, there 

 has been a segregation by some cementing agent that has 

 taken the form of a thin layer, or shell, having a spherical 

 outline. In weathering, this layer, being somewhat more 

 resistent to change than the rest of the stone, protects the 

 included portions, which thereby stand out in relief as 

 rounded objects. They can be seen in the cliffs of the River 

 Inman, nearly opposite the 8-mile post, and are known, 

 locally, as the "pots and boilers,' ' having the same popular 

 name as the serpuline forms in the Bermudas. They also 

 occur in the washouts, caused by small streams, in the sea 

 cliffs between Port Elliot and Victor Harbour, where they 

 were pointed out to me as "fossil pumpkins.' ' 



There is scarcely an appreciable difference in the com- 

 position of the material contained within the spherical shell 

 as compared with the general matrix of the till. The nature 

 of the cementing material which gives rise to this thin 

 spherical crust was not critically examined, but it is probably 

 of a ferro-siliceous kind, such as is often developed in 

 concentric lines and as "iron balls" in argillaceous sediments. 

 So far as observed, the size of these so-called "boilers" varies 

 from about a foot to two feet in diameter. 



There is little doubt that the serpulite rings that occur 

 in the shallow water of the coast at Encounter Bay take their 

 rise from this spherical structure which is developed in the 



