| OCR Text |
Show ~74 lM:BEDDlNG OF FltESH-W.A.TER PLANTS. (Ch. XVIl, of a quadrangu1 a r 1J! orm (fiOo'• g) • In Chara. hispidab which b nds in the lakes of Forfarshire, and w hlch has ecome fao sosuil in the Bakie Loch, each of the sp·i ra1 valves. of the seed-vessel turns rath er more than twice round the circ.u mfereTnche , the whole together making between ten and eleven n~gs. . e number of these rings differs greatly in different species, but m the same appears to be very constant. . Th t ms of charre occur fossil in the Scotch marl m great ab un deansc ee . In some species, as in Chara hi.s pida. , th. e plant w h en 1I.V 'In g contains so much carbonate of hme • m Its ve•g e- table orgam· zat 1' 0n, independently of calcareo. us mcrustatwn, that it effervesces strongly with acids ~hen dn.ed. rrhe stems of Chara h:ispida are longitudinally striated, wlth a tend~ncy to b . 1 These strire as appears to be the case With all e sp1ra . ' · 1 1 f charre, turn a 1w ays ll'ke the worm of a screw from ng lt to . e t, h.l those of the seed-vessel wind round in a contrary direc-wie · t t tion. A cross section of the stem exhibits a curious s rue ure, for lt is composed of a large tube surrounded by s~aller tubes, (dI. agram N o. Qo . fig • b' c ' ) as is seen in some extmct, as well (No.3.) c Stem and branchcl of Ohara l•upida. (a) Stem and bl·anches of the natural size. (b) Section of the stem magnified. . . f llertul.Jes, (c) Showing the central tube ~urrO\lnded by two tlllgs o ~ma Ch. XVII.] lMBEDDlNQ OF FRESH-WATER SPECIES. as recent species. In the stems of several species, however, there is only a single tube*. The valves of a small anima] called cypris (C. ornata Lam.) occur completely fossilized like the stems of charre in the Scotch travertin above mentioned. This cypris inhabits the lakes and ponds of England where it is not uncommon. Species of the same genus also occur abundantly in ancient fresh-water formations. The recent strata of lacustrine origin above alluded to are of very small extent, but analogous deposits on the grandest scale have been formed in the great lakes of North America. By the subsidence of the waters of Lakes Superior and Huron, occasioned probably by the partial destruction of their barriers at some unknown period, beds of sand one hundred and fifty feet thick are exposed, below which are seen beds of day, inclosing shells of the very species which now inhabit the lake f. But no careful examination appears as yet to have been made of recent fresh-water formations within the tropics, where the waters teem with life, and where in the bed of a newly drained lake the remains of the alligator, crocodile tortoise, and perhaps some large fish might be discovered. Imbedding of Fresh-water Species in Estuary and Marine Deposits. We have sometimes an opportunity of examining the de posits which within the historical period have silted up some of our estuaries; and excavations made for wells and other purposes, where the sea has been finally excluded, enable us to observe the state of the organic remains in these tracts. The valley of the Ouse between Newhaven and Lewes is one of several estuaries from which the sea has retired within the last seven or eight centuries ; and here it appears from the researches of Mr. Mantell, that strata of thirty feet and upwards in thickness have accumulated. At the top, beneath * Geol. Trans., vol. ii., second series, p. 73. On Fresh-water Marl, &c. By C, Lyell, Es<;t. t Dr. Bigsby's Journal of Science1 &c. No. 37, pp. 262 1 263, T2 |
