I would like to thank Anna Hutchens taking time out from her busy schedule to help with the motivation and editing of this paper. I would also like to thank Ian Jackson and John Fitzgerald for their constructive comments. I would like to thank the two reviewers Auke Barnhorn and Patrick Trimby for their constructive comments which improved the manuscript. Data collected at the University of Liverpool funded by a NERC research studentship tied to Grant Number NER/A/S/2001/01181. Sample deformed at the University of Manchester by Walliad Ismail.