Fossils are of interest for two rather distinct reasons. In the first place they tell about animals and plants which lived in the past, what they were like and how they had evolved. Secondly, they enable us to date rocks. The author tries to get fossils from the coal for his colleagues Kermack and Khne, who are palontologists rather than geologists. That is to say they are interested in fossils for their own sake rather than for dating. In order to date rocks you had better study the commonest fossil species, which are generally molluscs or other similar shellfish. The commoner types of shell from the coal measures are pretty well known. The fossil plants are also fairly well known, partly because there are a great many of them, as is natural since coal consists of plant remains, partly because they throw some light on how coal was formed, and have therefore been studied.