The effectiveness of trend-surface analysis when applied to geological problems has been greatly increased by the use of iterative-fit trend surfaces, in addition to conventional overall-fit surfaces, because the former surfaces generally satisfy a considerably higher proportion of the total variation than the latter, yet remain completely objective. Such trend surfaces have been used, together with conventional stratigraphical and sedimentological methods, in an analysis of the unusually thick and laterally-persistent cycle which lies between the Upper Hirst and Plean No. 1 coals and includes the Calmy Limestone. In the differentially-subsiding Kincardine Basin thin, laterally-impersistent coals and seatearths split the upper part of the cycle into a series of thinner cycles.
The regional sedimentation patterns of most of the variables studied are related to the pattern of total thickness of strata and hence to net subsidence. An exception is the Upper Hirst Coal which thickens fairly regularly eastwards. The sediments resemble those in modern deltas and reflect an initial widespread marine transgression followed by the readvance of deltas. A whole series of minor deltalobes or crevasse systems progressively filled up the basin until, in Plean No. 1 Coal times, coalswamp vegetation recolonized almost the entire area.