Besides that general conclusion with regard to the destruction of the strata, there is also in many places a demonstration of that fact, from a measured minimum of the quantity which had been removed.  It is to the mining business chiefly that we are indebted for that demonstration of which we now shall give an example.

The coal strata, about Newcastle upon Tyne, dip to the south-east at the rate of one in twelve, or thereabouts.  This is but little removed from the horizontal position; at the same time, the strata come all up to the soil or surface in a country which is level, or with little risings.  But in those strata there is a slip, or hitch, which runs from north-east to south-west, for 17 or 18 miles in a straight line; the surface on each side of this line is perfectly equal, and nothing distinguishable in the soil above; but, in sinking mines, the same strata are found at the distance of 70 fathoms from each other.  Here therefore is a demonstration, that there had been worn away, and removed into the sea, 70 fathoms more from the country on the one side of this line, than from that on the other.  It is far from having given us all the height of country which has been washed away, but it gives us a minimum of that quantity.

The examination of what is commonly called a secondary country is not sufficient to give us an idea of the immense operation of time in wearing the surface of this earth.  It is not that those countries of inferior hardness and elevation have been spared in the course of time, but because we have not, in those levelled countries, such great remainders, by which we are to judge the quantity of what is lost.  In the alpine country, again, though it be the same system of things with that which takes place in the lower country, the revolution of things is more marked for our view; and the ravages of time, in destroying the solid parts of the globe, in order to make soil of that which is removed, may be seen in all the steps of that important operation; whereas, in the more level countries, the scale of elevation is imperceptible, and that of time is so slow as renders our examination fruitless.  It is the Alps, therefore, chiefly that we are to take for an example, in tracing this operation of nature upon the surface of this earth, and forming some idea of the course of time that must have flowed during that operation in which the height of our land had been diminished.

On whatever side we approach the Alps, we find some great river discharging the waters which had been gathered above, and with that water all the waste of earth and stone which had been made among those lofty masses of decaying rock.  Now, we find this river running in a valley proportioned, in general, to this vehicle, in which is travelled the wreck of ruinous mountains.  Spacious plains attend those mighty streams; and, tho’ sometimes we find the greatest rivers much confined between approaching hills of solid rock, the valley opens again, and, on the whole, is always corresponding to the current of water which has successively run in all the quarters of this plain.  Here a question occurs; Has this valley been made by the operation of the river itself, or has it been the effect of other causes?  Let us now resolve that question.