| OCR Text |
Show 60 ERA OF THE OOLITE. kingdoms, but are always most conspicuous i_n fam1ltes approaching in character to those ~lasses to wlnch.the full organs are proper. This subject wtll be more particularly adverted to in the sequel. The highest part of the oolitic formation presents so!lle phenomena of an unusua:i. and interesting charactPr, wh!Ch demand special notice. Imm.edi3:tely ab?~e. the . upper oolitic group in Buckinghamshue, In the VICinity of Wey. mouth, and other situations, there is a thin stratum, usually called bv workmen the dirt-bed, which appears, from inconte~ table evidence, to have been a soil, formed, like soils of the present day, jn the course of time, upon a surface which had previously been the bottom of the sea. The dirt-bed contains exuvice of tropical trees, accumu .. lated through time, as the forest shed it~ honors on the spot where it grew, and l."lecame itself decayed. Near vVeymouth there is a piece of this stratum, in which stumps of trees remained rooted, moslly erect, or slightly inclined, and from one to three feet high ; while trunks of the same forest, also silicified, lie imbedded on the surface of the soil in which they grew. Above this bed, lie those which have been called the \Vealden, from their full develop1nent in the Weald of Sussex; and these as incontestably argue that the dry land forming the dirt-bed had next afterwards become the area of brackish estuaries, or lakes partially connected with the sea; for the \Vealden strata contain exuvire ot fresh water tribes, besides those of the great saurians and chelonia. The area of this estuary comprehentls the whole south-east province of Eno-land. A geologist thus confidently narrates the subsequent events : "Much calcareous matter \Vas first deposited, [in this estuary,] and in it were entombed myriads of shells, apparently analagous to those of the vi vi para. Then came a thick envelope of sand, sometimes inter tratified with rnud; anil, finally, muddy matter prevailed. The solid surface beneath the water:. ' ould appear to have sufrered a long continued and gradual d pr ssion, \vhich was as gradually filled, or nearly so, \'rith transported matt r; in the end, howe~er, after a depression of several hundred fe~t, the sea agmn entc1:ed upon the area, not suddeu ly or vwlentl~-for the Wealden rock pa s gradually into the supenncumbe~t. cretaceous series-but s quietly, that the mud conhunmg the remains of terrestrial and fr sh-water creatures was tran· ERA OF Tli£ CltETACEOUS FORMATION. 61 quihy covered 1lp by ~ands replete with marine exuvire."• A subsequent depresswn of the ~arne area, to the depth of ut least three hundred fathoms, Is believed to have taken pl~ce, to admit of the deposition, of the cretaceous beds lying above. Fro~ the s~attered way in which remains of the lar~er terrestnal animals occur in the 1Vealden, in the intermixt~ re of pe~bl~s or the special appearance of those worn in rivers, It Is also Inferred that the estuary which once cov. ered the southeast part of England was the mouth of a river of that far descending class of which the Mississippi and Amazon are examples. \Vhat part of the earth's surface presented the dry land through which that and other similar rivers flowed, no one can tell for certatn. It has been surmised, tl1dt the particular one here spoken of may have flowed from a point not nearer than the site of the present Newfoundland. Professor Phillips has suggested, from the analogy of the mineral composition, that anciently ele~ated coal strata may have c~"mposed the dry land from whiCh the sandy matters of these strata were washed. Such a deposite as the Wealden almost necessarily implies a loca.l n.ot a general condition; yet it has been thought that similar ~trata a~d remains exist in the Pays de Bray, near Beauvais. .This leads to the supposition that there may h.ave been, In that age, a series of river-receiving estauri.es along t~e border of some such great ocean as the Atlanhc, of which that of modern Sussex is only an example. ERA OF THE CRETACEOUS FORMATION. . TH:r: record of this period consists of a series of strata. tn which chalk beds make a conspicuous appearance and vy-hich is therefore called the cretaceous system or fo;mabo_ n. In England, a long stripe, extending from York .. ~hire to Kent, pr~sents the cretaceous beds upon the sur .. :lee, generally lymg conformably upon the oolite and in many instances rising into uold escarpments tow;rds the west. The celebrated cliffs of Dover are of this formation. It extends into northern France, and thence north-westward into Germany, whence it is traced Into Scandinavia "De la Beche's GeoloP"ical Researches, p. 344. |
