Cross‐strata of the Rough Rock (Millstone Grit Series) in the pennines

The Rough Rock is the highest sandstone horizon in the Millstone Grit Series (Namurian) in northern England. It is about 70 feet thick and outcrops over an area of some 4,000 square miles. Modal analyses show that it is an arkose, with about 20% of felspar (mainly microcline perthite) and many quartzose rock pebbles. Cross‐stratification is very common, occurring in sets mostly between one and three feet in thickness. The orientations of 1738 cross‐strata, measured at 301 localities, show that the currents flowed mainly southwestwards. It is suggested that the arkoses were deposited on an extensive and nearly horizontal floor just above sea level, and that sediment was distributed not by one but by many rivers, perhaps aided by flash floods.