Читать книгу Walking in the Yorkshire Dales: South and West. Wharfedale, Littondale, Malhamdale, Dentdale and Ribblesdale онлайн

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EVOLUTION OF THE LANDSCAPE

Geological history

The unique character and unquestionable charm of the Yorkshire Dales has its roots in the underlying bedrock, much of which was created during the Carboniferous period 300 million years ago. At a time when, in other areas, massive coal, gas and oil fields were being laid down in the accumulating detritus of humid forest swamps, the area which has become the Dales lay beneath a shallow tropical sea. Here, the broken shells of countless marine creatures settled to form a bed of limestone over two hundred metres thick. Known as the Great Scar Limestone, it dominates the scenery of the south western corner of the park and underlies its central core.

Eventually, river deltas encroached from the north, washing mud and sand across the coastal shelf. But this was a period of cyclically changing sea levels, creating sequential strata of shale and weak sandstones, repeatedly topped off by limestone as lagoon conditions intermittently returned. Each band is only around twelve metres thick, but the build-up over aeons formed a kind of layer cake over three hundred metres deep. Known as the Yoredale Series, because of its appearance in the valley of the River Ure – Wensleydale – it forms the basis of the northern portion of the park and extends further south as the higher peaks and ridges. The upper levels of this layering culminate in a hard, impervious sandstone known as millstone grit reflecting one of its uses and the remnants of this form the southern hill tops and the high ground of the northern fells.