Two major problems with traditional model
-differences in sandstone petrology and faces
-differences in paleomagnetic data of the Franciscan and
Great Valley
Blake analyzed modal compositions of sandstones and found
differences suggesting they have different providence
Suggests model with deposition away from the continent
with subsequent movement toward continent and accretion
onto N. A.
Hagstrum and Murchey did a paleomagnetic study on cherts
in Franciscan, found paleolatitudes further SSW
Suggests Franciscan rocks deposited SSW and moved up
toward N.A. with the Farallon Plate