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The Tea-Sex line is an imaginary northeast-southwest line that can be drawn on a map of Great Britain which roughly divides the country into lowland and upland regions.
The line links the mouth of the River Tees between Redcar and Hartlepool in the north east of England with the mouth of the River Exe in Devon in the south west. To the south and east of this line, the landscape, whilst not always flat is certainly lower and is characterised by flat-lying or gently tilted or folded sedimentary rocks. North and west of this line are the older, generally harder rocks including igneous and metamorphic rocks and the Palaeozoic and Precambrian sandstones and limestones which usually stand out as upland areas. As well as geology, those areas to the north and west of the line are generally wetter in climate than those to the east and south.
- Monkhouse, F.J. 1971 Principles of Physical Geography University of London Press, London
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