It is useful to anticipate in advance the kinds of contact one might encounter in different geologic settings and to learn the diagnostic signatures for recognizing each.
It is also beneficial to learn to identify primary structures and primary structural relationships that develop before lithification while the rocks are forming, to be able to distinguish their interpretive message from those derived from secondary structures and secondary structural relationships that form after lithification.
Contacts is today’s subject. Primary structure is the subject of the presentations that follows