96 THE GEOLOGIST. 
and houses, with their designs and purposes; but, if we stand on a 
j)innacle of the still higher spire of a cathedral, we cannot comprehend 
the details of the great city below us without a plan of its structure and 
the accompanying references to its principal edifices. Still more 
difficult is it to stand on the mountain -peak, and, even with a carefully- 
constructed map, to gaze over the apparently interminable ranges of 
hills upon hills, as they rise fainter and fainter in the grey distance, 
and to carry off in the mind a just comprehension of the scenery, or of 
the ever-varying characters of the country. How much harder, then, 
when our view is world-wide — and should, to be perfect, be world-deep 
also — for the mind properly to grasp the whole expanse. The outlines of 
the great territories of the past have been only partially mapped ; the 
references to the principal points may be correctly marked ; but where 
everything is toned down by regularity of succession, and by the 
obscurity of time, it is only the most prominent features or the great 
catastrophes and remarkable events that enable the perceptive faculties 
to conceive that frame- work into which they afterwards, by stud}"- and 
perseverance, fit the more ordinary phenomena, and fill up the spaces 
as a child fits in the intermediate slices of its puzzle. 
Of what are the ancient rocks composed ? — Of the beaches, sands, 
and ooze of the ancient seas and oceans, of the sediments of the rivers 
and lakes, of the vegetable and organic remains of successive and 
departed creations. Just as, on our coasts, we find the beaches, sands, 
and silts derived from the waste of the land, and the rivers bringing 
down to their lakes and estuaries the disintegrated particles of the 
soil and the produce of the earth. 
We see in the stratification of the rocks the evidence of such de- 
positions ; and we see in their materials the sources whence they were 
derived. 
We see in the drift-bedding of the ancient sands the efi'ects of 
currents piling up the shifting banks in the primeval channels ; we can 
measure the angles of the party-coloured layers of sand, as they incline 
to various points around ; and thus we can map the ancient shoals, and 
by the gentleness or the steepness of their slopes and by their other 
features, we can perceive whence the current came, how it rolled the 
particles along, and levelled off the tops of the banks. 
We examine the boulders and pebbles of the ancient conglomerates, 
and we match them with well-known mountain-rocks from far and 
