1852.] LYELL — BELGIAN TERTIARY FORMATIONS. 311 



posed them to be a part of the regular series, or Lower Limburg beds, 

 but M. Bosquet made excavations after we parted, which proved the 

 order of superposition to be as in the above section. He also found, 

 on washing the alluvial clay or loam, «, «', that it included many 

 Foraminifera of the Maestricht chalk, such as Rosalina depressa, 

 D'Orb., Siderolina calcitrapoideSi Lamk., &c.; alsoBryozoa, from the 

 same, of the genera Vincularia, Idmonea, Pustulopora, and others, 

 besides several Entomostraca, in all twelve cretaceous fossils. These 

 must have been brought down from the region between Tongres, 

 Liege, and Maestricht, or from the upper sources of the Damer, where 

 the Maestricht chalk exists, and the fossils were mixed up with those 

 of the denuded tertiary strata. The waters of the Damer must have 

 risen 40 or 50 feet above their present level to have deposited the 

 more elevated part of these modern alluviums. 



At Hoesselt a remarkable bed of pebbles, 1 ^ foot thick, occurs in 

 an analogous position, composed of well-rolled flint-pebbles, with an 

 abundance of large oysters {Ostrea ventilabrum) and other fossils. 

 This gravel rests on the Lower Limburg sands ; it is nearly horizontal, 

 and does not follow the slope of the ancient valley, scooped out of the 

 tertiary strata, which it has partially filled up. The shells which M. 

 Bosquet has found in it belong to no less than 49 species, by far the 

 greater part of them Middle or Upper Limburg species, and usually 

 much rolled ; whereas the Lower Limburg shells, especially the 

 smaller species, have suffered very little. Some of the flint-pebbles 

 in this gravel are 4 or 5 inches in diameter. At first sight the mix- 

 ture of freshwater and brackish water shells with rolled marine species, 

 reminded me of parts of the Woolwich pebble-beds belonging to the , 

 lower Eocene, near London. 



At Grimittingen also, and at Neerepen, I met with pebble-beds 

 overlying the Lower Limburg tertiaries, which M. Dumont refers to 

 the age of the Loess. They contain Cyrena, Pectunculus, and various 

 Middle Limburg shells, and some of them are with difficulty distin- 

 guishable from part of the regular series, which also, even where it is 

 undisturbed, as at Lethen, includes rolled flint-pebbles, and, as in the 

 case of the sands of Bergh, before alluded to (p. 306), rolled fossils. 



At Neerepen, the task of drawing the line between the incumbent 

 loess and the fluvio-marine tertiary beds is still more difficult. The 

 two deposits are laid open to view in a deep lane. The loess in its 

 upper part consists of a fine yellowish grey loam, as in the valley of 

 the Rhine ; and this was the only spot in Belgium where I found it 

 to contain Succinea ohlonga, which so generally characterizes it in 

 the Rhine valley, and Helix plebeial or hispidal. Still lower the 

 same species of land-shells are again seen, in a bed in which entire 

 Cerithia and other tertiary shells abound, so intimately blended, that 

 no geologist visiting the district for the first time would suspect them 

 to be of different ages. M. Bosquet found here an Elephant's tusk, 

 2 feet long, extending from the loess into the stratum full oi Cerithia 

 and tertiary shells. At a lower level is a pebble-bed, from 3 to 4 feet 

 thick, containing Corbida pisum, Pectunculus pilosus, Corbulomya 

 triangula, Cyrena semisti'iata, and several species of Cerithia. This 



