 To the south of Somerset there is an upland with a series of rolling valleys and scarps , from Penselwood in the east to the Blackdown Hills , another designated Area of Outstanding Natural Beauty , in the west . This is a geologically complex area of clays , limestone and marl . The honey @-@ coloured limestone at Ham Hill ( also known as Hamdon Hill ) is particularly important to geologists because of the assemblages of fossils which it contains , the sedimentary features which it displays and the way it relates to other rocks of equivalent age in the close vicinity . It has been quarried since Roman times at least . 
