rence of an outlier affords strong presumptive evidence of this inward dip, although the actual inclination of the beds may be so slight as to be inappreciable in a quarry.

Conversely, an anticlinal curvature, when denuded, often gives rise to what is called an inlier, which may be defined as the isolated exposure of an underlying bed amidst others which are geologically above it.

Figs. 156 and 157 are respectively a plan and section illustrating the occurrence of an outlier and an inlier. a A is an escarpment formed by successive beds of sandstone, shale, and limestone; o is an outlier of the limestone and shale, resting on a promontory of the sandstone, which is still connected with the main mass by a narrow neck. I is an inlier of the sandstone, within an inlying area of the shale, brought up by an anticlinal curve, and exposed in a

Fig. 157. Section along line s s.

valley excavated out of the long slope of the limestone. The section is taken along the line, s s, and illustrates the relations of the external features to the internal structure of the ground.

In the case represented by fig. 157, which has been sug gested by the structure of the Chalk Wolds of Lincolnshire, the outlier and inlier are caused by undulations parallel to the strike, but they are perhaps more often produced in nature by undulations across the strike, of the kind illustrated by fig. 81; the synclinals leading to the formation of outliers beyond the escarpment, and inliers occurring where the anticlinal folds happen to be crossed by some river-valley inside the main line of escarpment.

Among the older rocks which have been thrown into much sharper curves and contortions, outlying basins sometimes occur containing a great thickness of beds in their centre (see fig. 154), showing that a corresponding thickness must have been removed from the surrounding districts.

Flexures, however, are not the only conditions which give rise to the production of outliers and inliers. Faults, by causing an upthrow or downthrow of beds, may bring them into such positions that portions are afterwards isolated by erosion. Thus, if the beds in figs. 156 and 157 were traversed by a strike-fault along the line marked F F, instead of being bent into an anticlinal, an inlier might still be produced by erosion, though, in that case, its

Fig. 159. Sketch map of the Crich Hill District, by H. Carr, C.E. The arrows indicate observed dips. Scale, 1 inch to a mile.

western boundary would be formed by the line of fault. An inlier so produced is represented at c м, fig. 109, p. 363. This would be called a faulted inlier; and an outlier, similarly separated by a fault from the main mass, is called a faulted outlier. In such cases the inlier is always on the upthrow side of a fault, and an outlier is always on the downthrow side.

Occasionally it happens that a piece of ground enclosed by two or more faults has been bodily lifted up through a

certain vertical distance, and the upper beds being subsequently removed by denudation, the lower beds are more or less exposed, and form an inlier. Crich Hill, near Matlock, in Derbyshire, is an excellent example of such a faulted inlier. The appearance and structure of this hill are illustrated by the four following figures. Fig. 158 is a

Fig. 160. Geological Map of the Crich Hill District.
Scale, 1 inch to a mile. Dips shown by arrows.
The broken lines are faults.

1 = Limestone. 2, 4, 7 Shales. 3, 5, 6 Grits and sandstones.

view of Crich Hill from the river Derwent, whence it appears as a dome-shaped eminence, encircled by precipitous escarpments of less elevation than the central hill, the height of which is about 800 feet above the sea, and is crowned by a tower called the Stand.

The dimensions of this central hill, and its position with

1 Figs. 158 and 159 are taken from Mantell's "Medals of Creation."

regard to the surrounding escarpments, will be understood by reference to the sketch-map, fig. 159, which represents the physical geography of the district, while its geological structure is shown in fig. 160. A comparison of these two maps serves also to show the difference between an ordinary map or ground plan, and a geological map, on which the rock-structure of a district or country is delineated.

From fig. 160 it will be seen that Crich Hill itself consists of limestone, the beds of which are bent into an anticlinal curve, which becomes almost a periclinal at the north end of the hill. The surrounding escarpments are formed by the outcrop of several beds of hard grit and sandstone interstratified with softer shales, while it is along the course of the latter that the valleys of the district have been excavated. The dependence of physical features upon

Fig. 161. Section through Crich Hill.

geological structure is here, therefore, excellently illustrated.

From the map (fig. 160) it is seen that the country is traversed by two main lines of fault, which, together with a cross fault on the north-west, completely cut off the Crich Hill area from the surrounding district. The triangular tract bounded by these faults has been pushed bodily upwards, till the upper surface of the limestone (1) was raised above the level of the sandstone (6), as shown in the section (fig. 161) along the line, A B. Furthermore, during the process of erosion and denudation by which the physical features of the country have been produced, the whole of the beds, 2, 3, 4, 5, 6, 7, have been removed from the surface of the limestone that forms Crich Hill, so that this satisfies the definition of an inlier, and becomes a measure of the amount of the denudation that has taken place.

Such a section as fig. 161 is also useful as showing the