430 
TUE GEOLOGIST. 
Letter OH the Rapid Choking Up of TooU Harbour. By PiiiLir Brannon, C.E. 
Poole : R. Sydenham, lligh-strcct. 
Last year a letter was addressed to the quay trustees and coriwration of 
Poole on the state of the harbour there by Mr. Brannon ; the following ex- 
tracts from which give excellent illustrations of the rapid formation of sand- 
banks along a costal line, and as having a valuable bearing on some points 
connected with the rajnd formation of ancient sandstones. 
After many years close acquaintance with the coast in the nciglibourhood of 
Poole, the author is convinced that not only the bar, but even the whole of tlie 
sand-shoals are comparatively modern, and that tlieir formation has taken place 
with great ra})idity. His belief is that at tlic time of the Christian era the 
bottom was almost entirely of clay, ironstone, and other beds which now 
appear above the surface ; and that not only was the harbour capable of being 
entered in a straight line south-cast, but that over the site of the Hook there 
was free passage with a clay bottom below, precisely sbnilar to that found on 
sounding in a line with it otf Flag Head and the Iron Kocks. This state of 
things continued, as it appears to him, long after the Saxon times, and it is 
quite possible tiiat there wiis no considerable formations either of sand-banks 
below high-water mark, or wind-blown dunes above it, until long after the 
twelfth century, and ])robably even as late as the fifteenth. The cause of the 
formation of tiie Hook, and at a still later period of the bar, was the rapid in- 
roads of the sea on the coast eastward. As long as the sand-cliffs of the 
Branksome and Flag Head district stood southw^ard of certain lines of bearing 
with the Isle of Purbeek, all the sand which arose from the rains of the 
western cliffs was swept clear out to sea, and was deposited in the depths of 
the British channel. So soon, however, as the soft cliffs of that part were 
washed back within those luies of bearing, the sand brought down came more 
and more within the influence of the deflected and reflected currents or eddies 
between the ebb waters of the channel and those of the harbour ; and accord- 
ing to the invariable result in such cases was deposited in a yearly increasing 
ratio within the area of a delta, of which North Haven formed the north side, 
the channel ebb the south-east, and the harbour entrance channel the west. 
When this bank increased so as to rise above low water mark, during the ebb, 
tlie off-sea-gales drove up the sand on the shore, and thence formed the lofty 
dunes of the " Sand Hdls." At first the bank was probably quite in a line 
with High Horse Manger, and as late as Henry VIJI. the author believes 
there was very little sand deposited on the site of the present Hook. Every 
inch that Flag Head retired, however, gave the channel waters power to force 
these sand-baidcs north-westerly a great many feet. This vast bank of sand 
originally was formed, or at least deposited, in its present position in little 
more than one hundred and fifty years, or between the reigns of Henry Vlll. 
and Charles II., and that if any difference from this be the fact, it would be in 
favour of a much later and shorter period. But there will be no doubt as to 
the truth, when the following results are considered. Their significance, too, 
will be more clear, if we ])reviously remark that during the period which has 
since elapsed, nearly two hundred years, the harbour of Christehurch, theu 
deep, commodious, and of considerable capacity, has been entirely silted up 
and rendered useless, in the same way that Poole harbour wiU be, unless mea- 
sures both energetic and prudent be taken. 
The original direction of the entrance-channel was in the line of the baying 
in of the live fathom line, one and a-quarter miles south (magnetic) of Flag 
Head, and three quarters of a mUe cast of the northern red buoy, and bearing 
more than one and a-half miles east of the Handfast lime, or in a direction 
