of major ice-caps over the continents then clustered around the South Pole. Britain lay in the equatorial region. At times of high sea-level, silt and mud accumulated within the Pennine basin whilst at times of low sea-level, major deltas prograded across the region, their legacy being the thick sandstone beds of the Millstone Grit Group. Stratigraphy The Millstone Grit Group comprises over thirty individually named sandstones, some of regional extent, others more local in their occurrence. The intervening mudstones and siltstones are not generally named though important marine bands within them are named. The oldest, and hence lowermost in the succession is the thick Pendle Grit of central Lancashire. It is succeeded by the sandstone known variously as the Brennand Grit, Warley Wise Grit and Grassington Grit. These are all of Pendleian (E1) age – the lowermost sub-stage of the Namurian. The Lower Follifoot Grit, Silver Hills Sandstone, Nottage Crag Grit, Marchup Grit, Red Scar Grit, Ward’s Stone Sandstone, Cocklett Scar Sandstones and Dure Clough Sandstones are all assigned to the following Arnsbergian sub-stage. The Kinderscoutian includes the Kinder Grit, Longnor Sandstones, Shale Grit, Todmorden Grit, Parsonage Sandstone, Heysham Harbour Sandstone, Eldroth Grit and Ellel Crag Sandstone. The next sub-stage of the Namurian succession is the Marsdenian and it is to this that the Chatsworth Grit, Huddersfield White Rock, Holcombe Brook Grit, Greta Grits, Roaches Grit, Ashover Grit, Gorpley Grit, Pule Hill Grit, Fletcher Bank Grit, Brooksbottom Grit, Five Clouds Sandstones and Sheen Sandstones are assigned. The closing sub-stage of the Namurian, the Yeadonian includes the Lower Haslingden Flags and the last sandstone in the entire Millstone Grit succession known as the Rough Rock. It is a widespread unit which attains a thickness of around 45m though is more generally 15m thick. Economic importance Various of the sandstone beds of the Millstone Grit have been quarried for building stone, paving flags and roofing material. Its use in the construction of dry stone walls across the areas where it outcrops is considerable. In neighbouring limestone areas, gritstone has often been preferred in the past for use as gateposts and lintels. The very name of the rock derives from its widespread use within cornmills where it proved suitable for grinding stones. It also found agricultural use as drinking troughs for animals. The majority of the quarrying for such use took place along the eastern edges of the Peak District. Millstone Edge was