The Yorkshire Dogger

Extract

The Dogger of the coast from Peak to Kettleness is essentially a sideritic sandstone, and except in the Sandsend-Mulgrave district, is entirely unfossiliferous. This type of coast Dogger is well exposed at Hawsker Bottoms. To the naked eye it is a brownish sandstone of fine grain with very abundant white specks, a few small lenses of pale grey mudstone, and a very small number of bright green grains. Under the microscope it is seen to be a fairly well-graded sandstone with a few larger clastic elements, including both quartz and felspar as well as those mentioned above. The quartz grains are extraordinarily angular, doubtless due to corrosion by the matrix, and many of them are compound, i.e. microquartzites of various kinds. Felspar, mainly orthoclase and perthite, is abundant. A few flakes of chloritic chamosite and still more rare grains of typical speckled glauconite represent the green grains mentioned above. The matrix is somewhat oxidized, but still shows the usual well-formed rhombohedra of siderite, most of them with darker cores. The most notable point is that the sand grains rarely touch and are often widely spaced in the matrix, indicating simultaneous deposition of clastic elements and matrix, which is not a cement in the usual sense (Text-fig. 5). In this and in subsequent papers the term “ cement ” is used to connote that interstitial bonding material subsequently added to a bed of incoherent detrital grains which were lying in contact with each other before its infiltration : “ matrix ” is used for that interstitial material between detrital grains which are not in contact and which was therefore deposited contemporaneously with them, forming a part of the original sea floor deposit.