Stratification. 55 Strata vary very confiderably in the angle which they form with the horizon ; they occur from hori zontal to vertical, but the general inclination is be tween horizontal and 45 0 . The differences are either original, or have been produced by fubfe- quent changes. In ftrata coinpofed almoft entirely of mechani cal depolitions, any deviation from the horizontal pofition is generally to be confulered as caufed by a change of original pofition. We muff be care ful, however, not to confound highly inclined ftra ta of fandftone, with accidentally changed ftrata. This fandftone is in its original fituation, and it owes this fituation to the great portion of chemi cally diffolved matter combined with it, and the inclination of the bottom on which it is depofited. It may be laid, that the bottom on which it refts has been forced up while the ftrata were foft, and has thus given them their prefent fituation ; but this explanation will not fuffice, as thefe ftrata fometimes reft on walls of clay-fiate ; fometimes on loofe fandftone *, fometimes on faces compofed of horizontal beds of fandftone. In ftrata compofed of chemical precipitates, all the variety of inclina tion depends on the inequality of the bottom. If the bottom be very much inclined, fo are the ftra ta ; if it be very flat, the fuperincumbent ftrata are all'o flat. It is therefore a fad, that all inclined ftrata, with a very few exceptions, have been formed fo origi nally,