PrimcBval Rivers of Britain. 375 



lower jaw-bones, such as fall off from floating carcases in rivers, as 

 Dr. Buckland pointed out to be the case with dead dogs washed 

 down towards the mouth of the Thames. The Megalosaurus then 

 lived upon the land, as we know by his bones having been washed 

 into the neighbouring sea. 



When we examine the Purbeck strata, lying on the Portland 

 Oolite, we find thick beds of limestone formed of shells that lived in 

 lake and estuary ; and in one particular bed, mis-named a "dirt-bed," 

 but really an old lake-deposit, hundreds of bones have been found by 

 Messrs. Beckles and Brodie, that belonged to the land mammals and 

 reptiles of small size and various kinds, herbivores, carnivores, and 

 insectivores. The river-system that gave rise to the Purbeck beds 

 came from the west, as did the older rivers from the old land ; and 

 it continued in a modified form, and made the delta-beds, mud-banks, 

 sand-shoals, and lagoon-deposits, sometimes full of vegetable matter, 

 that are known as the Wealden formation. The Megalosaur lived on, 

 with the Iguanodon, Hylseosaur, and other monster reptiles of the 

 times ; and they not only left their drowned carcases as evidences of 

 their existence, but their foot-tracks remain on the marshy banks 

 now converted into sand and clay ; and these are often full of Palu- 

 dina, Cyclas, Unto, and other such-like shells, with ferns and cycads, 

 and other spoils of land and river. Similar deltas and lagoons ex- 

 isted in Europe and America, with the allied or analogous inhabitants 

 of the difierent regions. The sea again asserted its dominion over 

 these areas, and deposited the various Cretaceous strata, until, by the 

 silting up of the hollows, and by local elevations, land was again 

 formed, with its marshes, lakes, and rivers. Of these the lignites 

 and wonderfuUy-mammaliferous strata of Nebraska and the adjacent 

 regions bear full witness ; and the South of France is said to have 

 similar passage-beds between the Cretaceous and the Tertiary systems. 

 Since then, that is, during the Tertiary period, and until now, conti- 

 nental areas, the nuclei of the present continents, have existed, with 

 varying outlines and elevations, and with glaciers and river- systems, 

 which have left numerous fresh- water formations. The "Woolwich 

 beds are the oldest of these. The London clay, lying on the last- 

 mentioned, was the mud of a great gulf, receiving, perhaps, the same 

 river, with others, draining a land rich with a sub-tropical flora of 

 conifers, palm, spice-trees, etc., and stocked with crocodiles, serpents, 

 birds, and mammals. A modification of the same drainage system 

 afterwards washed the Paleeothere and many other land animals into 

 the seas and lakes of the subsequent period, as we see in the Barton 

 Cliffs, in the Isle of Wight, and in the Paris district ; for the Num- 

 mulitic sea came and went, and oscillations of the land changed the 

 levels, and fresh water alternated with salt on many coasts. The 

 middle Tertiary times had a still more chequered scene of sea and 

 land ; for bays, straits, archipelagos, rivers, lakes, and glaciers 

 abounded. The Dino there, Mastodon, and other land animals, great 

 and small, and a characteristic flora, have been preserved here and 

 there in lake-deposits of that time, often in beds of great extent and 

 thickness. 



