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Show , EMIGRANT'S GUIDE. . none is so commonly used, and none so productive of er~m· as simi. larity of lati tude. The difference .often perc ived to ex 1 ~t between the temperature of two places, which to c:1sual o b~e r.v ;.1t10n w~m ld have little or uo local distinction, ought to teach cautiOn to wnter · anJ observe rs on this subject. It has been seen, whrn describing- t 1e r ivers of tbe st<ltc of Ohio, that their streams ~ppc a r to be prec" pitated from a high ta )le land. \tVhen lelineatin<r west Pennsylvani:t and w 'St Vir;(nia, tbe saltiC 11 atural features ;ill exhibit themselves. From which it is ernon~ trable, th at the actual Led of the Ohio i ~ much lower tharJ the tlllJie land from whence the tribu tary streams of thi riv _r draw tb ei a· w a~ ters. The actual diHcrence in elevation bns not IJct!n ~c cur atcly t.l ctermin ed. Dr. Drake surposcs the extreme elevatinn of the ccnt1al plains of Ohio, Indiana, and lllinois, to be au ut 1000 f et above tbe level of the water in the Atlantic; but there i · good reason to suppose that those plains are at least 1200 feet alJOve tbc level of the oc '<ln. If Tirow nsv ille is 850 feet above tide water in the Chcsa eal e b:1y,·x- th apex of the adjoining hills being at least 400 feet higher t 1an tlJc level of the Monongahela at the latter town, must be 1290 or 1300 feet above the level of tide water. The a~thor of this treatise measured car£.:fully the difference of elevation between the level of the Monongahela river, at tbe city of Pittsburg, and the surrounding hills, and found the difference about 460 feet. The fall in the river from Brown. ville to Pitt!)burg, must be 50 or 60 feet. \iVhile engageu in measuring the elevation of the hills near Pittsburg, one fact appeared to obtrude itself at every operation ; that was, that the apex of these hills , and indeed tbose of the whole country, west of the chestnut ridge, were very nee1rly equal; and th at the whole region had once been table land, into ·which the descent of water had , in the lapse of ages, cut tbe valleys that now exist. This fnct is also proved by the phenomena of corresponding strata, p~rticularly of coal. The coal stratD. near Pitt~burg maintain v 'ry near y a level with each other, and were evidently once united; they arc 340 feet above low water mark in the rivers that environ Pittsburg. Not only the coal, but all the other ~trata present mark~ of continuity. ,.fhe course of the Ohio river from Pittsburg to the mouth, is gentle; except the rapids at Louisville, 22 1-2 feet in two miles. ,.fhc entire I ngth of the Ohio and :Mississippi from Pittsburg to the Gulf of Mexico, is 2040 miles ; which would yield, by allowing only 5 inches fall per mile, 350 feet as the elevation of low water mark at Pittsbuq?;, above the level of the Gulf of Mexico ; which sum adtled to 460 feet, produces 1310 feet as the entire elevation of the summits of the hills on west Penn· ~ylvania and west Virginia. An abrupt descent, of more than onethird the whole uepression , produces an immediate change in atmos~ pheric temperature. [n the. low vale of Ohio, and in such places as Cincinna i, \'l'here plan s are presented to a southern, and sbelter~d from a nor bern exposure, inflorescence will take place at very Jif· fQrent se~sons, and fruits must always be precocious when comparoJ.. * l>raki's Cincinna.ti, page ~. EMIGRANT'S GUIDE. I 233 :\'ith vegetation in situations .however near, which are exposed to the chilling effects of north winds. From these causes arise the local difference between flowering, "seed time and harvest," at Cincinnati, and 40 minutes of latitude to the nortb of that town, on MaJ river. From the same cause , the entire table Iandi from the northwestern side of the Aleghany mountains to the Canadian Jakes, being open to tbe north and cover cl from the south winui, must necess<lrily h:1ve a coluer climate than places on corresponding latituues on the Atlantic coast. Assuming vege table life and the effects of frost upon rivers as the true criteria upon which to judge of the relative temperature of different places, it will be seen from the data given not only by Dr. Drake, but all other writers on the subject, that Cincinnati is more exposed to winter cold than Philadelphia, though the former place stanJs upon the globe 51·' of lat itude south of the latter. It has already been observed i'l1 this tre tise,* that there exists an extraordina· ry discordance between the facls and inductions of writers on this subject ; the following extracts will exhibit the correctness of this assertion. " The piercing northerly winds that prevail during the winter in the Atlantic states, seldom affect the inhabitants on Cumberland river; for they have no great mountains to the northwtlrd or westward. The inhabitants of the Atlantic states are also subj ect to sudden changes in the atmosphere, arising from their vici11ity to the ocean. The air thaf comes from the surface of the sea, espec-ially frorn the war·m. gulf s~ream in winter, must be very different in its tem perature from the a1r that comes across colu and Mgh mou'lJtains; but the great distance between the Cum be rl and settler5 anJ the ocean, as many areat mountains intervene, effectually screens tbem against the bad effects of those sudden changes. Northeasterly storms never reach this coUJa· try."t The facts stateu in this quotation are substantially correct, except the latter. Northeast storms are violent and frequent, even at Natchez. l t certainly must excite some mrprise to read in the same paragraph, that the warm winds from the surface of the gulf stream, should produce colu, and that an exposure to north winds, heat. Mr. Stoddard, in his historical and descriptive sketches on Louisiana, t. obse rves, that, " The settlements in that country, (now Missouri terntory,) are between the 33° aud 40° north lat. The winters among them are much more severe than in the corresponuing latitudes on the sea coast. They generally set in about the 20th of November aud continue to near the last of February; though hard frosts, and even snow, are common in October and March. For three successive wiuters, commencing in 1802, the ~\iississippi at St. Louis was passa- 1le on the i~e before tbe twentieth of December each year; and it was clear ot all obstruction, with only one exception, by the last of * See page 147. t PM01·se's Universal Geogl'aphy, page 524, sixth edition. age 236, 30 I |