216 THE GEOLOGICAL STEUCTURE OF THE 



tion, whereas the deposit during the same length of time at 

 Frocester Hill, ascertained by S. S. Buckman by some recent 

 measurements, is as much as 264 feet in thickness. 



3. The Dumo7'tieria-heds. 



It is certainly rather singular that the inappropriate 

 nature of the term " Midford Sands " from a lithological 

 point of view should be shown by a locality so close to 

 Midford as is Dundry Hill. The distance from Midford to 

 Maes Knoll is only 10| miles; yet the deposit which would 

 be called "Midford Sands " at Dundry is a clay — the "D?t- 

 mortieria-heds " — resting upon a thin ironshot limestone, and 

 this latter deposit is contemporaneous with some 30 feet of 

 the lower portion of " the Sands " at Midford. 



With a thickness of 'some 50 to 60 feet the clays of the 

 Dumortieria-hed are to be found all round Dundry Hill, 

 immediately below the limestone series or so-called "Inferior 

 Oolite ; " and they may be known by such surface-indications 

 as fruit-trees, springs of water, and so on. 



The Dumortieria-heds are, in point of date, contempor- 

 aneous with the middle portion of the Cotteswold Cephalopod- 

 bed, and, judging by the evidence at North Stoke, ^ near 

 Saltford, with the upper part of the Midford Sands. ^ 



1 North Stoke is 7 miles from Maes Knoll eastward. 



2 The name " Midford Sands " has been applied in a wide sense to 

 certain sandy deposits which were supposed to intervene between what 

 was called Inferior Oolite above and Upper ^Lias below. But these 

 sands have been shown to be non-contemporaneous, so that the deposit 

 of the same date was called Upper Lias at one locality, Midford Sands 

 at another, and Inferior Oolite at a third. Therefore it is necessary to 

 use the term Midford Sands, in a retricted sense as a local name for 

 certain sandy beds in the neighbourhood of Bath. The other sandy 

 deposits also bear local names for precision. The different dates of 

 these Sands may be seen in our Table III. 



