162 E. E. L. Divxwon— 
The chief questions that arise are :— 
1. Were the hollows in the limestone formed before or after the 
deposition of the beds spoken of as Millstone Grit ? 
2. What is the age of the so-called Millstone Grit ? 
1. The catenary bedding of the sandstones shown in PI. II (a) 
suggests at first sight subsidence into a local hollow formed after 
their deposition. The remainder of the evidence is, however, 
overwhelmingly against this conclusion. The sandstones have been 
deposited as sand in their present position, and have not been 
disturbed since consolidation. They contrast strongly with the 
debris of Millstone Grit filling swallow-holes, both recent and pre- 
Glacial, in the Carboniferous Limestone at various places in South 
Fig. 2.—Diagrammatic sketch of a cavity in Carboniferous Limestone (L.), 
filled with sandstone (G.) and shales (S.). 
Wales; in these the sandstones and shales are broken, or even 
thoroughly shattered, and jumbled together. The evidence that the 
Ifton sandstones have not been disturbed since consolidation needs 
to be unearthed in the field to be fully appreciated. It consists 
partly in the unbroken character of the hard beds, straight and 
curved alike, which are too brittle to bend, partly in the fact that 
the wedge-like form of some and the minor details of the lamination 
of others (as at M, Fig. 1) have been obviously determined by 
adjacent limestone-surfaces, and partly in the firm welding of some 
to the enclosing limestone. 
2. The Lepidophloios ? was certainly deposited contemporaneously 
with the enclosing sandstone and was not part of a derived fragment. 
But this genus merely shows that the beds are Carboniferous. The 
lithological and stratigraphical evidence, however, is fairly 
conclusive. The choice of horizon lies between some part of the 
