Geology of the Isle of Purbeck. 271 



Although retaining its beauty under protection, it soon loses 

 its polish exposed to the atmosphere. The middle contains 

 numerous layers, fresh and marine. Several species of mam- 

 mahan remains have been found in this section ; but the most 

 conspicuous feature is the "cinder" bed, 12 feet thick, com- 

 posed of a mass of Ostrea distorta, and which can be well studied 

 in Durlston Bay. Shells of Cyrena also occupy another thin 

 bed. The lower Purbeck is remarkable chiefly for its "dirt" 

 bed, with its remains of Cycads and coniferous trees. Layers 

 of gypsum can also be well seen from the shore. 



The quarries from which the Purbeck stone is dug are 

 scattered all along the hill side above the town, and consist of 

 sloping well-like holes of no great depth, up the sides of which 

 the blocks are drawn by a windlass. Sheds for squaring the 

 curbs and flags stand by the mouth, and the whole is generally 

 surrounded by a low wall. Each quarry is worked by two or 

 three men ; and I was informed by an intelligent native that the 

 trade is fast dwindling down, owing to the clannish and con- 

 servative habits of the miners, who resist any change or 

 suggestions for co-operation and improved machinery. Many of 

 the quarries that I visited were unworked, which seemed to bear 

 out the statement. 



At Durlston Head we come to the Portland stone, a tongue of 

 which extends eastward to this point, and forms a facing to the 

 Purbeck. It is well seen all the way to St. Aldhelms Head, 

 about 5 miles distant. The cliffs, though not high, are vertical, 

 rising abruptly from the sea and exhibiting square-shaped caves, 

 and are the haunt of many sea-birds. Some open quarries of 

 this stone exist along the coast, and produce huge ammonites 

 and oysters. In smooth weather boats can be moored alongside, 

 and the stone lowered directly into them by a crane. 



On some of the hill sides in this neighbourhood are a number 

 of artificial parallel terraces. The only suggestion I can find as 

 to their origin is in a paper, by Canon Isaac Taylor, describing 

 the cultivation of ancient lands by ridges. Whatever the ground 

 formerly produced, it is now only used for sheep grazing. 



Beyond St. Aldhelms — or St. Albans Head, as it is sometimes 

 called — the land recedes to Chapman's Pool, which is the entrance 

 to a deep narrow gorge running inland. At the base of these 

 hills appears the celebrated Kimmeridge clay, gradually rising 

 westward, and productive of many fossils. Large ammonites 

 are very abundant, and may be seen projecting from the cliffs. 

 Many species of marine shells exist, and where the clay is hard 

 sphts up easily, showing their remains, but generally in a 

 fractured condition. One species, however, Astarte . . . . , I obtained 

 in a better condition, as it appears to be always imbedded 

 vertically to the line of cleavage. On the shore I picked up part 



