372 Notices of Memoirs — Prof. T. Eupert Jones. 



it in suspension nntil the current is checked in the still water of a 

 lake, or of a broad reach or bend of the river, or in the sluggish 

 delta-streams where they commingle with the sea. And even here 

 the sweeping tides may drive on the clay-stained waters for many a 

 league, until, transferred to the quiet of a land-locked bay, they drop 

 their sediment, or, borne out to depths where nothing else can reach 

 but drift-wood and floating shells from shore, it slowly sinks among 

 the creatures of the deep. 



Where clay has settled near a river's mouth, it is often associated 

 with the decaying marsh-plants, drifted trees, and the water-logged 

 leaves of successive autumns. Where rain-floods and freshets of 

 snow-water have periodically deluged the river's course, the sediment 

 will include the carcases and bones of drowned land animals, and 

 the mud-choked water-creatures that lived at and near its mouth. 



What rivers do now they have always done, since the land began 

 to be drained of atmospheric waters along the cracks and crevices of 

 the strata, and the old creeks and arms of the retiring seas. Whether 

 the ground was left by the sea as flats and table-lands, planed hori- 

 zontally by "marine denudation," or still rugged with the inequalities 

 of crumpled strata crushed upwards by the contracting crust, the air, 

 rain, snow, and frost have had to reduce the elevated and to fill up 

 the hollow surface. And amidst the many changes that this ter- 

 raqueous globe has suffered (changes due mainly, perhaps, to the 

 reaction of internal heat on a cooling and contracting crust, with its 

 shifting loads of water-borne sediments), such varied deposits as 

 those of everchanging river-systems, rising in the high lands, lifted 

 up in each successive period, and depositing their loads of mud as 

 stratified sediments in the corresponding water-areas, were always 

 being made and often swept away again, but sometimes buried under 

 other strata and kept as part of the stratified series, as we see it now. 



The characteristic sign of fluviatile and lacustrine strata have been 

 indicated above, and the kinds of shells, such as Paludina, Limnceus, 

 Planorhis, Ci/rena, Cyclas, Unio, Anodon, etc., are well known. So also 

 Cypris and Estheria among the low Crustacea have left their carapace- 

 valves in the silts of fresh or brackish waters. Fishes are not good 

 witnesses ; for many genera and even species of fish inhabit both 

 rivers and sea, and may be imbedded in the mud of either. Accumu- 

 lations of vegetable matter (especially land plants) are more likely to 

 occur in lakes and rivers than in the sea ; and the skeletons of land 

 animals get dissipated as separate bones in most instances before they 

 reach the sea. In Shells, Corals, and Encrinites we have the best 

 criteria for judging of the origin of strata. There are fossil beds of 

 shells, such as Paludina, that are never known to live in the sea ; and 

 there are others, as Ostrea, that flourish only in salt water, though 

 some individuals may have a struggling existence in brackish estuaries. 

 Others, as Venus and Turritella, are sea-shells. Of Entomostraca, 

 Cythere, Bairdia, Leperditia, and others are habitually marine. Of 

 Corals there are none that live in rivers or lakes; and all fresh waters, 

 too, are destitute of Echinoderms, whether Starfishes, Encrinites, or 

 other forms, as well as of Foraminifera, the microzoa so abundant in 



