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Table 2 lists values of t for different values of V. The values of V were chosen corresponding to the volumes of fluid expelled from an overpressured 40km x 2kmm thick sediment sequence at depth with incremental changes in porosity of 0.1, 1 and 10\% on dewatering. These approximate to the width and thickness of shale in the Carboniferous Edale basin to the north-east of the Derbyshire platform. The porosity changes range from the smallest incremental changes calculated for individual dewatering pulses of overpressured sediments to the integrated maximum volume of fluid that might be expelled \citep{Cathles:1983tj}. The corresponding values of t are 67, 6912 and 694000 years respectively. These correspond to mean effusive fluxes of 136, 13.2 and 1.3 litres.hr^{-1} for every metre length of the fault. Such flow rates are not geologically unrealistic. The highest rates associated with the smallest fluid pulses are on the order of the rates of effusion from springs that have been monitored for periods of several years following moderate earthquakes e.g (add refs by Nur and Tsuneishi et al., 1970).  One can legitimately question the model details and parameter estimates but the point of this somewhat heuristic approach is not to be an accurate model. Rather, it is to give an indication of the flow rates that are needed to sustain the maximum observed thermal anomaly within the Dirtlow Rake assuminga physical system that couples fluid overpressure  and flow. to assess whether these are reasonable.  That the model may only be accurate to within a factor of 5 to 10 does not invalidate the central result that if fluid release occurs in a pulsed and episodic manner then each event must be of short duration to sustain the necessary thermal anomaly. A corollary of the pulsed nature of fluid release is that mineralization is episodic with separate events spanning limited periods up to several thousand to several ten thousand years separated by periods of stasis. This observation is convergent with recent data on the Zn content of mineralizing fluids determined from fluid inclusions in several MVT provinces that suggests mineralization events could be of durations as short as 10,000 years \citep{Bodnar:2009hc, Wilkinson06022009}.