ersities 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. The Upper Rhine
flows in one of these great valleys of subsidence for about 180 miles,
from Mulhausen to Frankfort, in a generally straight line, though
modified by denud