What is formed on top plate B?

Without specific context regarding what "plate B" refers to, it's difficult to provide a precise answer. In general, the formation on a top plate can depend on various factors, such as environmental conditions, materials involved, or processes occurring. For example, if it's a geological context, sediment or mineral deposits could form. If it's in a laboratory setting, a chemical reaction might lead to the formation of a compound. Please provide more details for a tailored response.