376 PALAEONTOLOGY. 



led Professor Henslow* to call the attention of agricultural 

 chemists to the red crag as a deposit of valuable manure. 

 Since that period it has yielded a large supply, worth many 

 thousand pounds annually, of the superphosphates. The 

 red crag is found in patches from Walton-on-JSTaze, Essex, 

 to Aldbro', Suffolk, extending from the shore to 5 or 15 

 miles and more inland. It averages in thickness 10 feet, 

 but is in some places 40 feet. Broken-up septarian nodules 

 form a rude flooring to the crag, left by the washing off 

 of the London clay, and called " rough stone." The phos- 

 phatic fossils, or " cops " as they are now locally termed, occur 

 in greatest abundance immediately above the " rough-stone." 

 Thousands of cubic acres of earlier strata must have been 

 broken up to furnish the cetacean nodules of the " red crag." 

 This is a striking instance of the profitable results of a seem- 

 ingly most unpromising discovery in pure science, — the deter- 

 mination of what in 1840 was regarded as a rare, unique, and 

 most problematical British fossil.t 



Our knowledge of the progression of mammalian life 

 during the miocene period is derived chiefly from continental 

 fossils. These teach us that one or two of the generic forms 

 most frequent in the older tertiary strata still lingered on the 

 earth, but that the rest of the eocene Mammalia had been 

 superseded by new forms, some of which present characters 

 intermediate between those of eocene and those of pliocene 

 genera. The Dinotherium and narrow-toothed Mastodon, for 

 example, diminish the interval between the Lophiodon and the 

 elephant ; the Anthracotlwrium and Hippoliyns, that between 

 Chcerojjotamtts and Hippopotamus; the Acerotherium was a 

 link connecting Palwotherium with Rhinoceros; the Hippo- 

 therium linked on Paloplotlierium with Equus. 



One of the most extraordinary of the extinct forms of the 



* Proceedings, and Quart. Jour. Geol. Soc, 1843. 

 f History of British Fossil Mammals, 8vo, p. 536, 



