Abstract: Based on previous study results made by other researchers,this paper works over the tonstein from the chemical composition point of view,by means of main element analysis,trace element analysis and rare earth elements analysis.The result not only makes it further sure that the coal parting of kaolinitic claystone in the study area was formed by the alteration of volcanic ash fallen into the peat moor,also the authors put forward a new idea,according to the results of microelement analysis and REE analsis,that the forming of the coal parting was likely to be influenced by different kinds of volcanic material erupted in not exactly the same period of time,which provides a new way to thinking in the study of volcanic event sediment in coal-bearing measures.