360 Sheppard: The Kellaways Rock of South Cave. 
The transition from the red sandstone to the white cal- 
careous type is sometimes abrupt, yet such a change is char- 
acterised by a suite of either Ammonites or Rhynchonelle 
which have been perfectly preserved. In many cases compact 
‘pockets ’ of Rhynchonelle, for example, are found constituting 
the nucleus of the lighter coloured patch. Probably the 
organic acids generated by the decomposition of such a col- 
lection of animal matter in the first case had accelerated the 
process of cementation and assisted in the accretion of calcium 
carbonate. 
Microscopically, the sandstone consists of grains of quartz, 
some of which are well rounded, while the remainder are of a 
sub-angular variety. Sharp outlines of the quartz crystals 
are not common, suggesting that all had been subjected to 
a certain amount of secondary denudation before the ultimate 
consolidation’ took place. Comparing with the other types 
of the same rock the constituent grains are loosely arranged 
in a brown matrix of oxide of iron and lime carbonate. In the 
lighter patches the percentages of iron diminishes and is re- 
placed by a mosaic of calcite. Hence from a microscopical 
point of view the only important difference between the ordin- 
ary sandstone and its associated lighter variation is that in the 
former type brown or opaque oxide forms the matrix to the 
exclusion of calcareous shells, while in the latter calcite replaces. 
iron oxide, and occasional well-defined sections of bi-valve 
shells occur. 
Other minerals noticed were—orthoclase, plagioclase, micro- 
cline, biotite, calcite, limonite and rutile. 
The quartz grains are usually traversed by strings of in- 
clusions (e.g., in the Millstone Grit) and, where fractured, the 
crack has been filled in by the oxide of iron. The corroded 
edge: of several. of the quartz grain suggest the type so pre- 
valent in certain of the rhyolites and felsites. Needles of 
rutile were also present in occasional quartz grains. The 
orthoclase, a rare constituent, was of a turbid nature and the 
edges were largely corroded and in an advanced state of 
chemical decomposition. 
Plagioclase (of the Albite type) occurred, though in a 
clouded state. One feature of the section, however, was the 
occurrence of microcline, which appeared to be quite fresh and 
shewed no evidence of deterioration. The characteristic 
‘ cross-hatching’ was particularly well-defined under crossed 
Nicols. Under a high power very small globules of iron oxide 
were observed enclosed in the calcite crystal. The only other 
mineral of importance was'a pseudomorph of augite which was 
largely chloritised ; sufficient of the original crystal, however, 
was left to shew its cleavage. 
In the Doggers there are several distinct and interesting 
Naturalist, 
