  It is shown that coassociative cones in R^7 that are r-oriented and ruled by
2-planes are equivalent to CR-holomorphic curves in the oriented Grassmanian of
2-planes in R^7. The geometry of these CR-holomorphic curves is studied and
related to holomorphic curves in S^6. This leads to an equivalence between
associative cones on one side and the coassociative cones whose second
fundamental form has an O(2) symmetry on the other. It also provides a number
of methods for explicitly constructing coassociative 4-folds. One method leads
to a family of coassociative 4-folds whose members are neither cones nor are
ruled by 2-planes. This family directly generalizes the original family of
examples provided by Harvey and Lawson when they introduced coassociative
geometry.
