Page:A Treatise on Geology, volume 1.djvu/35

 CHAP. I. of the arrangement of strata, in a part of the crust of the earth.





If the globe were conceived to be cut through, the section near the surface would show a number of layers variously inclined to the horizon as in fig. 4., so as to come up to the surface in succession a, b, c, d, &c.; not, as in fig. 3., parallel to the horizon, as many persons are apt to imagine. The thicknesses of a, b, c, d, &c. separately, may be easily known by pits and wells, or natural sections in ravines or precipices; their order of succession may be found by the same means, and thus the total thicknesses of all the stratified rocks visible in any one country, may be easily known by direct observation. By a judicious selection of examples, the upper part of the series of strata may be measured in one district, as a, b, c, d, fig. 4, the middle in another, which contains the lower portions of the former series, as d, e, f, g, in fig. 4.; and the inferior portions in a third, fourth, &c., so as to complete one general table or section of the whole series of strata visible in an island, or continent; and, finally, on the face of the whole globe.

This labour is actually accomplished for many large portions of the globe; and it is found that the stratification of the matter of the earth ceases at some depth which is not the same at different places, three, five, ten, or more miles below which are rocks of different structure, aspect, and origin, and not stratified.

Here, then, is the limit of our knowledge, from actual inspection and exact induction of facts