By Charles Moore, F.G.S. 53 



Kimmeridge Clay is almost entirely argillaceous, whilst the Portland 

 Sands are as distinctly arenaceous. These pass into the limestones 

 of the series, and all are marine. But the Purbeck beds above are 

 either brackish or have been deposited by fresh water. The con- 

 sequence of this has been an almost entire change in organic life, 

 which could only have been brought about by a great lapse of time 

 in their formation. They have but small development in Wiltshire, 

 occurring as outliers at Bourton and Swindon, and again at Chicks- 

 grove and Tisbury. At Portland, and on the coast at Swanage, they 

 have their chief development, the Purbeck beds alone — which at 

 Swindon are but about 10 feet thick — being there estimated at 300 

 feet. These beds, including those of the Wealden above, with 

 which they are intimately associated, have in their full development 

 a thickness of 2500 feet, and Professor Ramsay suggests that they 

 are the lagoon or delta of an immense river then continuous through 

 a continent as large as Asia, rivalling in size the Ganges or the 

 Mississippi. That it was bounded by dry land, which now seems 

 to have entirely disappeared, is evidenced by the fact that its in- 

 significant representative at Swindon has yielded to me the remains 

 of terrestrial marsupial mammals, reptiles, insects, and vegetation, 

 that were caught up and re-deposited by its waters. On the 

 Dorsetshire coasts the Purbeck beds have yielded not less than ten 

 genera and and twenty-five species of land animals. How interesting 

 it would be if we could go back and stand upon the banks of this 

 mighty river and realize all the physical changes it would indicate ! 

 I need scarcely say that crowded as are the Chalk beds of this 

 country with organic remains, there is still good work to be done 

 with them. Warminster and its neighbourhood has always repaid 

 examination. As I have not worked in these beds I must pass on 

 and shall only refer to conditions immediately preceding or contem- 

 poraneous with the dawn of our own era. At this time, though no 

 doubt there have been some modifications in the outlines of our hills 

 and valleys, their forms were generally what they now present. But 

 their climatic conditions were altogether different; periods of ex- 

 treme cold, with alternating intervals of higher temperature. These 

 are included in the Glacial Period, within which were deposited our 



