We will now leave the coast district for a time and climb the plateau edge to survey the country beyond. First let us consider the nature of the obstacle by which the early settlers were faced. The Blue Mountains are merely a part of the eastern rim of a great tilted tableland of sandstone, with a steep face towards the sea and a long and more gentle slope towards the west. Down this face a series of comparatively short streams come tumbling to the sea; while on the other side of the ridge, almost within sight of the sea, are the sources of the slow westward-flowing rivers, whose courses are measured by thousands of miles. In this sandstone block the torrents have carved out deep gorges, which often widen out up-stream into broad valleys; but these valleys are deceptive and do not provide a road to the interior, 17 since they end in steep cliffs over which the streams plunge in waterfalls. Here is a view of the country at Govett’s Leap; 18 we may notice the flat tops of the ridges, all about the same level, which suggest the old surface of a plateau. It was a long time before the early settlers found a path over this edge, and the available roads are still very few all along its length, as we may see by tracing them on the map; our train must twist and tunnel up one of the ridges between two of the valleys by a most difficult route, with steep inclines, instead of following the bank of the stream below. We realise that climbing a plateau is a far more serious matter for the engineer than piercing through a narrow ridge of mountains.