This peculiar heat-distribution, together with a much smaller mass and gravitative force, would lead to a very different development of the surface and an altogether diverse geological history from ours, which has throughout been profoundly influenced by its heated interior, its vast supply of water, and the continuous physical and chemical reactions between the interior and the crust.
These reactions have, in our case, been of substantially the same nature, and very nearly of the same degree of intensity throughout the whole vast eons of geological time, and they have resulted in a wonderfully complex succession of rock-formations--volcanic, plutonic, and sedimentary--more or less intermingled throughout the whole series, here remaining horizontal as when first deposited, there upheaved or depressed, fractured or crushed, inclined or contorted; denuded by rain and rivers with the assistance of heat and cold, of frost and ice, in an unceasing series of changes, so that however varied the surface may be, with hill and dale, plains and uplands, mountain ranges and deep intervening valleys, these are as nothing to the diversities of interior structure, as exhibited in the sides of every alpine valley or precipitous escarpment, and made known to us by the work of the miner and the well-borer in every part of the world.
_Structural Straight Lines on the Earth._ The great characteristic of the earth, both on its surface and in its interior, is thus seen to be extreme diversity both of form and structure, and this is further intensified by the varied texture, constitution, hardness, and density of the various rocks and debris of which it is composed.

It is therefore not surprising that, with such a complex outer crust, we should nowhere find examples of those geometrical forms and almost world-wide straight lines that give such a remarkable, and as Mr.Lowell maintains, 'non-natural' character to the surface of Mars, but which, as it seems to me, of themselves afford _prima facie_ evidence of a corresponding simplicity and uniformity in its internal structure.
Yet we are not ourselves by any means devoid of 'straight lines' structurally produced, in spite of every obstacle of diversity of form and texture, of softness and hardness, of lamination or crystallisation, which are adverse to such developments.

Examples of these are the numerous 'faults' which occur in the harder rocks, and which often extend for great distances in almost perfect straight lines.

In our own country we have the Tyneside and Craven faults in the North of England, which are 30 miles long and often 20 yards wide; but even more striking is the great Cleveland Dyke--a wall of volcanic rock dipping slightly towards the south, but sometimes being almost vertical, and stretching across the country, over hill and dale, in an almost perfect straight line from a point on the coast ten miles north of Scarborough, in a west-by-north direction, passing about two miles south of Stockton and terminating about six miles north-by-east of Barnard Castle, a distance of very nearly 60 miles.

The great fault between the Highlands and Lowlands of Scotland extends across the country from Stonehaven to near Helensburgh, a distance of 120 miles; and there are very many more of less importance.
Much more extensive are some of the great continental dislocations, often forming valleys of considerable width and length.