How might mudcracks be preserved in rock? Crossbedding? Shell impressions? HINT: Review how ripplemarks are preserved.
Would the presence of such features serve to distinguish between sedimentary and volcanic layers? HINT: How likely do you think it is that mud, sand and shells would survive immersion in lava?
Look at the two pictures under 'Useful Structures' that show mudcracks. Is the origin of mudcracks similar to the origin of columnar jointing? Explain. Hint: Mudcracks form due to shrinkage, but the shrinkage in NOT due to cooling. What might be lost from mud to cause shrinkage?
Can columnar jointing be used to identify volcanic layers in the absence of volcanic cones? HINT: Does any other type of layering contain a feature similar to columnar jointing with which it could be confused?
Both mudcracks and lava that has undergone columnar jointing both have networks of fractures. How might mudcracks and lava flows be distinguished? HINT: What differences might there be between dried mud and solidified lava? Think texture. Think composition.

© 2001, David J. Leveson