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Show 224 CTIRONOLOGICA L COMPUTATlONS OF the C1 1 anO'eS W1 l l.C 1 1 tl 1 ey llavc underOo' one since the last series of convulsi~ns which agitated and altered the face of the.country. The probability, thet·efore, of crrot· in our.chronologi~a~ .com- putatw. ns, w1 1 ere we omit to pay due attent.i On to these cucum-stances, increases in proportion to the ttme that may have e1 a pse d s·m ce ti1e last disturbance of the country by subterra-ncan moveme nts , and l. n proportion to the extent of the hydrographical basin on which we may happen to speculate. The Alpine rivers of Vallais are pre;ented at present from con· tributing theh· sedimentary contmgent to the. delta of the Rhone in the Mediterranean, because they are mt~rcepted by the Leman Lake ; but when this is filled, they will transport as much, or nearly as much, matter to the sea as they now pour into that lake. They will then flow through a long, flat, alluvial plain, between Villeneuve and Geneva, fro~ two to eight miles in breadth, which will present no superficial marks of the existence of a thickness of more than one t1~ousand feet of recent sediment below. Many hundred alluvial tra~ts of equal, and some of much greater area, may be seen 1f we follow up the Rhone from its mouth, or explore the valleys of many of its principal tributaries. . What, then, shall we think of the presumptiOn of De Luc, Kirwan, and their followers, who confidently. ~educed from the phenomena of modern deltas the recent o~1gm of the pre~ sent form of our continents, without pretendmg to have collected any one of the numerous data by which so complicated a problem can be solved? Had .they, ~fter making al~ .the necessary investigations, succeeded 111 provmg, as th ~y desued, that the delta of the Rhone, and the new deposits at the mouths of all other rivers, whether in lakes or seas, had r~quired about four thousand years to attain their present dt· mensions the conclusion would have been fatal to the chrono] oO'ical tl;eories which they were anxious to confirm. ~he poop ular recepti'o n of these, and similar sop ln'~ ms, respec t 1n (oJ' the effects of causes in diurnal action, has hitherto thro~vn slumbling·blocks in the way of those geologists wl~o des.H·c to pursue the science according to the rules of mducti~e Philosophy. If speculations so vague and visiona~-y can c proposed concern.m g natura1 operati·O ns .now p.a 's·s m.( oJ' bef.o re our eyes--if authors may thus dogmatize, With Impumty, TilE AGE OF DELTASi 225 on subjects capable of being determined with considerable degree of precision, can we be surprised that they who reason on the . more obscure phenomena of remote ages, should wander m a maze of error and inconsistency * ? The Leman. Lake fills a great cavity in rocky strata, composed of a tertiary conglomerate and sand, which constitutes its bottom, almost a~l its ~orthern banks, and a great part of its sou~hern or Alpme side. It has often been asked, why this cavity has not been filled up by the detritus of rocks, removed from the numerous va1leys now drained by the waters which enter the lake? In order to remove this difficulty, it would be necessary to enter into a description of the strata of different ages compo~ing the. Alps and .the Subalpine districts; to point out the distmct penods of their elevation above the sea and the pre-exi.s tence o f many mountain valleys, even to the fo' rmation of those deposits wherein the Lake of Geneva is contained. It would be pre~ature, therefore, to enter upon this subject at present, to whiCh we shall revert when we have described the phenomena of some of the ancient strata. Laic~ Superior.-Lake Superior is the largest body of fresh water m the world, being about one thousand five hundred geographical miJes in circumference, if we follow the sinuosities of its coasts, its length, on a curved line throuO'h its centre b. b ' emg about three hundred and sixty, and its extreme breadth one. hundred .and forty geographical miles. Its average depth van:s from e1ghty to one hundred and fifty fathoms; but, accordmg to Captain Bayfield, there is reason to think that its greates~ depth would not be overrated at two hundred fathoms-~, . so that Its bottom is, in some parts, nearly six hundred feet below ~he level of the Atlantic, as its surface is about as much above It. There are appearances in different parts of this, as of the * It is an encouraging circumstance, that the cultivators of the science iu our own country have begtm t o apprec1.a t c tl1 e t rue vaI ue of the prm. c1. plcs of rcasom. ng most usually applied t I . I . . . . . 1830) 1 . , 0 goo og1ca ~ucshons. Wlul~ wr1tmg tins chapter (April, tl ' . happ~.ncd to attend a meehng of the Geological Society of London where 1e prcs1dent 1 · .1 .1 ' .1 '. lil us auuress, made use of the expression, a 11eologica/ lonician. A sm1 c was seen tb t v members like co·n .e coun enances of some. of the a.u dience ' wh.il e many of the th ~ . Icero s augurs, could not res1st laughmg ; so ludicrous appeared 0 associatiOn of Geology anu Logic. + Trans. of Lit, and Hist. Soc, of Quebec, vol. i., p. 5, 1829, Vot. I. Q |