The Alderley Sandstones
The upper division (ex-Keuper) follows the lower (ex-Bunter) unconformably. The upper is very thick and in Cheshire reaches a thickness of about 1250 m, locally conglomeritic, but consists mainly of fine water lain sandstones.
Interest in the area took off with vigour in the mid-19th century with the first real efforts made to quantify the strata of the country using the new mapping methods that geologists like William Smith had pioneered. The economical value of the area in those times lead to a detailed examination of Alderley. Boreholes starting to be used for geological logging and research whereas previously they had been used simply for wells with no real interest taken in the actual geological make up of the rock below. In 1894, a borehole was sunk to 280 ft below surface and the strata recorded in a scientific manner. This borehole, the Isaac Massey (NGR SK 84237819) was the first serious attempt to understand the geology of the area. The area has since been subject of much more detailed research and still provides many clues to basin formation and mineralization processes. The original borehole was crude by today’s standards but it gave an overview of the strata below the Alderley area.
Now the Wilmslow Formation, (part of the Sherwood Sandstone Group), the lower Triassic was previously a threefold division, the Lower Mottled Sandstone, The Pebble Beds and the Upper Mottled Sandstone, (only the later is seen at Alderley) which merged into the Conglomerates of the upper Triassic. The Upper Mottled Sandstone now the lower Wilmslow Member is a medium to coarse-grained friable false-bedded sandstone with abrupt colour changes from bright red to white. It is composed mainly of rounded grains but sub-angular grains also occur. Normally the rock lacks coherence and weathers into sand down to 6 m and even unweathered rock can be crushed to sand easily. However near faults, ghost crystals of barites make the sandstone harder and resistant.
Read more about this topic: Geology Of Alderley Edge