Acknowledgements

Preliminary discussion with A. Wetzel and R. Bromley are acknowledged with thanks. M. Sutton kindly provided initial guidance in the art of serial grinding and tomographic reconstruction. Material from Cajiloa, Baja California, was collected with B. Kneller, whose help and logistical support are much appreciated. Support for this research came from an NSERC grant to DMc, the SLOPES consortium and the award of Canada Research Chair to DMc. We would like to recognize the contribution of Dr. Wetzel and an anonymous reviewer, which helped us to clarify our arguments.