THE GEOLOGIST. 



Letter on the Rapid Choking Up of Poole Harbour. By Philip Beani^on, C.E. 

 Poole : R. Sydenham, High-street. 



Last year a letter was addressed to the quay trustees and corporation 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 rapid formation of ancient sandstones. 



After many years close acquaintance with the coast in the neighbourhood of 

 Poole, the author is convinced that not only the bar, but even the whole of the 

 sand-shoals are comparatively modern, and that their formation has taken place 

 with great rapidity. His belief is that at the 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-east, but that over the site of the Hook there 

 was free passage with a clay bottom below, precisely similar to that found on 

 sounding in a line with it off Flag Head and the Iron Rocks. This state of 

 things continued, as it appears to him, long after the Saxon times, and it is 

 quite possible that there was no considerable formations either of sand-banks 

 below high-water mark, or wind-blown dunes above it, until long after the 

 twelftli century, and probably even as late as the fifteenth. The cause of the 

 formation of the 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 Plag Head district stood southward of certain lines of bearing 

 with the Isle of Purbeck, all the sand which arose from the ruins 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 lines 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 norl h 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, 

 the off-sea-gales drove up the sand on the shore, and thence formed the lofty 

 dunes of the " Sand Hills." At first the bank was probably quite in a line 

 with High Horse Manger, and as late as Henry YIII. the author believes 

 there was very little sand deposited on the site of the present Hook. Every 

 inch that Plag Head retired, however, gave the channel waters power to force 

 these sand-banks 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 liundred and fifty years, or between the reigns of Henry VIII. 

 and Charles II., and that if any difference from this be the fact, it would be in 

 favour of a much loiter and shorter period. But there will be no doubt as to 

 tlic truth, when the following results are considered. Their significance, too, 

 will be more clear, if we previously remark that during the period which has 

 since elapsed, nearly two hundred years, the harbour of Christchurch, then 

 deep, connnodious, and of considerable capacity, has been entirely silted up 

 and rendered useless, in l lie same way that Poole harbour will 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 five fal liom line, one and a-quarter miles south (magnetic) of Plag 

 Head, and tlu'ce quarters of a mile east of tlie northern red buoy, and bearing 

 more than one and a-lialf miles east of the Ilandfast line, or in a direction 



