Dynamic analyses of deformed quartz and calcite from the Swift Formation at Dry Creek Ridge anticline, Montana, were made to test the method for determining orientations of principal stress directions from microstructures produced by intragranular flow in quartz and the homogeneity of principal stress orientations around a fold. Close correspondence of results with Turner's (1953) calcite technique indicates that quartz may be used independently for dynamic analysis. Arguments presented suggest that under the ambient conditions of deformation (about 1 kb overburden pressure, 100 degrees to 150 degrees C), the stress difference of slip in quartz was probably as low as that for deformation of the calcite aggregate. Orientations of deduced principal stress axes around the fold are remarkably consistent. In consideration of regional structure, the orientations of principal stress directions probably reflect bending stresses in the compressive part of a very thick plate.