74 The Geology of the Portland Pror)iontory, 



was met with in the second bore, and no chalk, although it 

 is likely that the latter would have been reached within a 

 short distance further down, as elsewhere, a shallow deposit 

 of red and blue clays overlies it.* 



For instance, a Mr. Smith has sunk to obtain water in his 

 strawberry garden, near to the Bridgewater Road, and 

 within the Borough of Portland. He tells me that after 

 passing through beds of red and blue clay, and then through 

 a shell bed, the bore entered the chalk, and struck water at 

 a depth of thirty feet. At this spot there is no eolian lime- 

 stone, and the surface stratum is a very thin deposit of 

 decomposed lava. 



The centre of the Portland Promontory is occupied by a 

 low range of hills, known as Bat's Bidges. These hills are 

 an extension of this limestone formation, and they are 

 perforated by many caves, some of which are of consider- 

 able length. Professor Tate has assigned this limestone for- 

 mation to the pleistocene period, and while the Rev. Julian 

 Woods sBjs that it is pliocene, Mr. Dennant describes it as 

 '' Recent." 



VI. — The Recent Formations — the Sand Dunes. 



Sand dunes occur in long narrow strips, bordering those 

 portions of the coast which are exposed to the strong south 

 westerly winds which prevail here. 



Their spread inlan^d appears to me to be an exceedingly 

 recent movement, due to artificial causes. Mr. Kennedy 

 who has resided at Bridgewater for forty years, tells me 

 that when first he came to the district, the sand dunes were 

 very much narrower than they are now, and that their 

 surfaces were then bound down by various grasses. These 

 began to be eaten down when cattle were introduced, and 

 the coastwise traffic commencing simultaneously, the dray 

 wheels destroyed the roots left by the cattle, and so let loose 

 the sand. By these means the surface features of the parts 

 adjacent to the coast have been greatly altered of late years. 



The dunes are composed of comminuted shells, mixed 

 with a little siliceous sand. The materials are coarser than 

 those which compose the false-bedded limestone, and they 



* Had these operations been conducted under the dhection of any one 

 with geological knowledge, the bore would have been started in the 

 neighbourhood of the Botanical Gardens, at Portland, in the chalk. The 

 money was wasted in putting a bore through the limestone at Nelson Bay. 



