Sheppara: The Kellaways Rock of South Cave. 361 
differences. The concretions themselves almost defy all at- 
tempts at fracturing even with a heavy sledge hammer. They 
consist of a light, grey, compact sandstone, the constituent 
grains being so small as to be indistinguishable to the naked 
eye. It presents a sugary fracture and has almost a quartzitic 
nature. 
If a piece of the broken rock be turned in the hand, vaiious 
glancing surfaces of fairly large size are at once conspicuous and 
are typical examples of ‘ lustre-mottling.’ Occasional discolora- 
tions of brown oxide occur, but are extremely rare in a true 
“ Dogger.’ The matrix of these concretions consists of much 
finer particles of sand. Organic traces are rare in a true con- 
cretion of the Dogger type. 
Considered -microscopically, a typical section presents a 
compact aggregation of angular quartz fragments of a very 
small and uniform size. They possess a definite arrangement 
in the matrix, and appear to have a regularity which is quite 
absent in the previous type. Iron traces are scarce and the 
grains are so closely packed together that the matrix is difficult 
to make out under ordinary light. Under crossed Nicols, 
however, a different interpretation is presented. The whole 
section practically consists of a series of calcite crystals which 
have enveloped the constituent sand grains. Whole patches of 
calcite, giving brilliant series of high polarisation tints, are ob- 
served enclosing the sand particles after the manner of the 
well-known Fontainebleu Sandstone. Thus a pure calcitic 
matrix has been formed and partially re-crystallised into a 
mosaic of prisms. This explains the glancing effect observed 
in the fractured hand specimen, and the peculiar ‘ lustre mott- 
ling.’ In addition to the quartz and calcite, other minerals 
observed were felspar and biotite, both of which were in a 
decomposed state. Specks of green chloritic material were 
also noticed but these may have originally been flakes of mica 
which had suffered alteration. Tourmaline is present in the 
sandstone, though only a solitary fragment was seen. 
Probably the Doggers themselves are due to pockets or 
accumulations of fine material which bear a certain relation to 
the underlying Kellaways sand of the same section. 
It has been assumed that the predominant dark colour of 
the Liassic clays is the result of the denudation of great areas 
of the Coal Measures which persisted during the deposition of 
the Lower Jurassic strata. 
Similarly, would not the denudation of the Millstone Grit 
in Jurassic time result in a deposit similar to that of the 
Kellaways Rock? Comparing the respective natures and 
characteristics of both the Millstone Grit and the Kellaways 
Rock, the latter presents a type such as would be expected 
from the denudation and subsequent deposition of the former. 
1913 Oct. 1. 
