A large amount of burrow fossils are found in peliticsiltstone in the middle Changzhougou Formation of the Mesoproterozoic in the Yanshan area.
在燕山地区中元古代常州沟组中发育有大量的潜穴化石,潜穴产于常州沟组中部的泥质粉砂岩中。
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Its main rocks is the metamorphic peliticsiltstone, the feldspathic quartz wacke, the fine sandial feldspathic quartz siltstone, the feldspathic wacke and the sericite quartz phyllite etc.