Ixxviii. 



ST. JELDHELM'S HEAD. 





tfl 



formation. They recognised that because the tops 

 of these beds, being of very soft Weald clay, were 

 easily denuded by the weather, which in the course 

 of ages cut it in a sort of trough, lying between 

 Corfe Castle on the north and these southern 

 Purbeck hills on which they were standing now. 

 On top of the Wealden Beds was the interesting 

 deposit of tufa at Blashenwell, which unfortunately 

 they had not time to visit that day. Next to the 

 Wealden they came to the most interesting beds in 

 that part of the country, especially associated with 

 their excursion that day the Purbeck Beds, so 

 named from the Isle of 1'urbeck, in which they 

 were developed to a greater extent than in any 

 other part of England. Of the stone from these 

 Purbeck Beds they had interesting specimens in the 

 churches which they had visited, notably the 

 columns of Purbeck shell-marble. These Purbeck 

 Beds were first seen between Peverel Point and 

 Durlston Head, where there was the finest exposure 

 of the Purbeck Beds in the world, of great value on 

 account of the limestone which they produced, and 

 of still greater interest to geologists, because in 

 them had been found remains of the earliest 

 mammals tiny little mammals about the size of 

 rats. They were now standing 011 St. Aldhelm's 

 Head on a thin cap of the Lower Purbeck Beds, 

 which were at one time continuous, stretching 

 right over the head and away to sea for miles and 

 miles. And no doubt, if they could follow those 

 beds, they would find them lying beneath the 

 waters of the English Channel. The Purbeck cap 

 lay upon the Portland stone, which was also of 

 great commercial value as well as of geological 

 interest. The Portland stone lay upon a similar 

 thickness of Portland sand, and that again upon the 

 Kimmeridge clay soft black tenacious clay which 

 was of no value commercially, although it ought to 

 be of great value, because in certain parts it was 

 saturated with animal oils derived from the remains 

 of saurians, which existed in countless myriads when 

 these strata were being laid down at the bottom 

 of the sea. Consequently it made excellent manure. 

 Again, before American petroleum was introduced, 



