366 THE DEPOSITS. 



clays (chalk derived) is ossiferous, but here we have no animal 

 remains. In both we have the lower boulder clay, and hence 

 have to decide only where the ossiferous deposit belongs. We 

 are assisted in this determination by the deposits in the 

 English caves and rock fissure which contain the same animal 

 remains and can place them in series between the two clays. 



The " Head " is a collection of deposits (the remains of 

 the original deposits) that have taken the whole Pleistocene 

 Period to form. 



By means of these deposits we are able to trace the order 

 of events. Thus, there are sands the time of the 25 feet 

 beach, of the 50 feet beach, and there are sands of the period 

 separating the clays, and we find that the upper and lower class 

 are separated by a laud surface. 



Some of the inland deposits, on account of their associa- 

 tion with the beaches, are described as passage beds, but these 

 may also have their equivalents in the heads. At Miellette 

 Bay (see Diagram No. 13) the deposits are such as are 

 described by Professor Prestwich as " Head," and yet they 

 contain marine sands not to be found on the cliffs, but are 

 correlated by the deposit of the upper clay and by a presumed 

 old earth surface. 



In order to give the proper value to the " Head " it will 

 be necessary to show the different types of " Head " to be 

 found here (and in the other islands) and describe their modes 

 of formation. 



1st. -AERIAL. 



These have been formed at all times and in all places 

 where there has been sufficient height and steepness of cliff to 

 permit of the fall of the loosened rock. An example of this 

 " Head " is to be seen at Bon Repos and at Les Tielles as 

 well as in several adjoining cliffs. 



The process to be seen is both rapid and extensive. At 

 Bon Repos the base of the cliff has advanced on the top of the 

 beach quite six feet since I began to observe it. (Photo- 

 graphs Nos. 13 and 14.) This type does not depend on the 

 sea at all, for it may and does occur inland. The require- 

 ments are a soft and decomposed rock with its joints parallel 

 to the exposed face. Where this " Head " falls on a beach it 

 appears in the section, where it falls on land it becomes 

 covered over and is lost to sight under later falls. An 

 example of the latter is to be found at several places on the 

 old cliff above Pleinmont Point. There are examples of this 

 type to be found along the cliffs Avhere they tell of the 

 occurrence of elevated conditions. These are intermediate 



