Goodness - 40 ANDYSEZs! (Well actually 37). How time flies - have I really been writing these things for over ten years? I wonder how many times I have missed Kent's deadlines?

Last time I promised you some discussion on epikarst and egg cartons (perhaps that should be egg karstons?). Well, I haven't got round to doing the necessary observations so that will have to wait. And I don't have the energy to tackle Cave Mineralogy part III.

When I was in Korea I had a spirited discussion with my colleague Prof Kyung Sik Woo and his friend from Gosudongul about some clay vermiculations in Tanyang Chon Cave. Vermiculation is the term used to describe "thin, irregular, discontinuous deposits consisting of incoherent materials (usually mud and clay) commonly found on the walls, ceilings and floors of caves" (Hill and Forti 1997, page 221). Because of the connotations of "incoherent" with speech a better adjective might be "unconsolidated". Common types of vermiculations are shown in the accompanying diagram from the first edition of Cave Minerals of the World (Hill and Forti 1986).

Vermiculations are soft and easily damaged. They are usually found only on smooth rock or speleothem surfaces. They are quite common but often overlooked. They range in size from millimetres to centimetres in length but are usually only a few millimetres wide and thick.

In spite of earlier explanations attempting to involve plants and animals in their formation they seem easily explained by invoking the wetting and drying of water films containing particles in suspension in the film or floating on its surface. The form of the vermiculation is determined by the ratio of water to particles. If there is little water to particle volume a mud film will result. If the ratio is the other way round, as the water film evaporates the material will be deposited as spots or fine lines often surrounded by a fine halo of the parent material produced as the vermiculation shrinks during its final drying. And, as usual, there is a spectrum of forms!

Although this apparently simple mode of development is a pleasant change, we must look to a variety of factors influencing the final shape of the vermiculation. These might include bedrock shape and texture, type of particles, evaporation rates and possibly more exotic things such as electrostatic effects.

As noted above, they are common world-wide. Their apparent ubiquity in Australian caves may lie in two factors. Firstly, we frequently have fairly strong cycles of wetting and drying in our caves. Secondly, there are relatively high levels of dust in our atmosphere - especially in drought periods and we may be seeing more dust brought frequently into our caves than is common in wetter climates. It is tempting to invoke dust from Mongolia and China for the Korean examples - but that might also be manufacturing unsupportable hypotheses!

Dust from visitor traffic and other tourist-derived deposits such as lint can contribute to vermiculation development in show caves and one can view their formation actually happening following a cave washing exercise.