123 
ing the sea it was dashed to pieces and ground up by wave action 
into fragments of all sizes. These fragments were sorted by 
gentle currents and tidal ebb and flow, and deposited amidst the 
sand and mud at the river-mouth. 
Perhaps the most significant evidence of marine influence 
exerted near the mouth of a great river is afforded by 
the trunks of conifers and the masses of coniferous wood 
frequently formed in the cliffs. (Plate XVII. Fig. 2). I hey 
occur all along the section, but are especially common 
after heavy gales, when the fore-shore has been much 
disturbed by wave action. Then, at low tide, fragments of black 
lignite of all sizes up to two or three feet long may be found 
in abundance. These are nearly always teredo-bored, the holes- 
being usually filled by green pyritized sand or mud. They are 
difficult to preserve, usually splitting and crumbling away by con¬ 
traction on drying. In the sandy beds in the cliff face occasionally 
large tree trunks, many feet long and sometimes a foot in 
diameter may be seen. These are usually very fragile and crumble 
to the touch. They are riddled by teredo borings, which are filled 
with sand. Occasionally in a mass of sand may be found sandy 
or clay casts of teredo borings, which resemble worms or worm 
casts, these represent all that is left of what was once a tree 
trunk, the woody matter having entirely vanished or remaining 
only as a trace in black lignitic sand surrounding the casts. All 
this woody material in the various forms described was formerly 
drift-wood floating about in the estuary of the river and in back¬ 
waters or side-channels. The same phenomenon occurs to-day at 
the mouths of great rivers, especially when these are obstructed 
by mud-banks and shallows. The wood is rapidly attacked, bored 
through and through by the teredo, until sometimes a mere shell 
of wood remains, this becomes water-logged and sinks. The holes 
then are filled up by mud or sand, and the fragments buried in 
the river deposits. The great quantity of this wood found in our 
Bournemouth beds testifies to the size and importance of the 
ancient river, and to the richly wooded country through which it 
must have flowed in its course from the west. 
At “ Steps Chine,” as it used to be called from Meyrick 
steps which led to the beach before the present Zig-Zag Path was 
made, imperfect casts and impressions of mollusca were found 
on an occasion when the beds were less obscured by slips 
than usual. This was rarely the case in Mr. Gardner’s time, and 
I have never been fortunate enough to find any. Probably they 
occurred in a local patch, which has long since fallen. It was 
possible, however, to recognise an Ostrea, Area, Modiola , Tellina, 
Natica , and Cerithium , and in a lower bed a Unio -like shell. These, 
with remains of Callianassa and a shore-crab, are evidence of the 
transition to marine conditions from those of the upper beds, and 
confirms the opinion that here (and for some distance eastward) 
mud and sandbanks obstructed the river-mouth and retained much 
of /the vegetable debris brought down by it. 
