I have examined the evidence cited in support of Maxwell's hypothesis of dewatering as the origin of slaty cleavage. Study of critical exposures of cleavage associated with clastic dikes cited by Maxwell fails to show the necessary parallelism between the two structures. Measurements made on the cleavage-dike pairs gives a mean dihedral angle of 14°.
Other evidence cited in support of dewatering is ambiguous either in terms of finite strain considerations or alternative explanations offered by the pressure-solution hypothesis. I conclude that as yet no evidence of substance has been produced in support of the dewatering hypothesis.