Retaining wall below Ardencaple Tower
The tower itself is not well seen from here, but it is shown in
Image, and summarised in the end-note. Click on the end-note title for related pictures of it.
In the present picture, the tower itself is obscured by the tree on the left, but the main point of the picture is not to show the tower, but rather its setting. Housing built here after 1957 has changed the area greatly, but the retaining wall still makes it clear that the tower occupies a position at the top of a precipice.
The geology of the area and its influence on the choice of this location for the castle were described very well by George Campbell, the 8th Duke of Argyll, in his autobiography. The relevant passages are as follows, where I have added a couple of links to illustrate the geological features that are mentioned:
"One special feature of the whole estuary of the Clyde was conspicuous at Ardencaple. That feature is an 'old coast line' which marks a higher level at which the sea used to stand, and must have stood for ages, from about 30 to 60 feet above the present level of the sea. This old coast-line is marked by a steep bank (
Image), sometimes rocky, with caves (
Image) eaten out by the waves, or with projecting ledges undercut by passing sheets of ice.
The distance at which this bank stands back from the present line of the shore depends, of course, on the contours of the land. When those contours are steep, the distance is often very small; where they are gentle and gradual, there may be large and nearly level fields separating the old from the present coast-line. In the Middle Ages all sudden declivities were more or less valuable for the purposes of defence, and fortified houses were often built upon this line of steeps.
...
The old castle of Ardencaple had been built on the crest of the old coast-line, at a point where it was very steep and formed a projecting curve, so that the walls could have the benefit of a natural defence on two sides."
["Autobiography and Memoirs of George Douglas, Eighth Duke of Argyll, K.G., K.T. (1823–1900)", (2 vols; London; John Murray, 1906).]