8 LOWER OOLITIC KOCKS OF ENGLAND : 
very sharply defined, and cut through individual grains of oolite. 
By the action of weak acids, the grains were dissolved and the 
coatings left intact, forming beautiful objects for examination 
under the microscope. In both cases the matrix itself was colour- 
less and transparent. (See Plate I., p. 26, fig. 4.) 
In the Corallian Beds again we have the oolites that are locally 
replaced by iron-ore, as at Westbury and Abbotsbury. (See 
Plate II., p. 29.) 
Sometimes the grains occur in a calcareo-arenaccous paste, as 
in certain layers of the Stonesfield Slate, and in sandy beds of 
Corallian age. In the Forest Marble we have the oolitic grains 
disseminated amid comminuted fragments of shell, furnishing 
evidence of some reconstruction or reassortment of material. 
Petrological Notes on the Oolitic Rocks. By J. J. H. Teall, 
F.R.S. 
The Limestones. 
These rocks exhibit considerable variations in colour and 
texture... Some are nearly pure white, others bluish-grey, others 
again cream colour, buff, yellow, or brown. Yellow and brown 
tints are especially characteristic of surface-rocks, and are 
evidently due to the oxidation of the iron present in bluish-grey 
varieties, such as are found in deep well-borings (e.g., Great Oolite 
of Streatham), and in the interior of blocks from deep quarries. 
Having regard to texture, and the character of the recognizable 
constituents of the rocks, we may distinguish three principal 
types; compact, shelly and oolitic. The compact varieties are 
.seen, by the aid of the microscope, to consist essentially of ex- 
tremely minute granules of calcareous matter, and may be 
regarded without lear of error as resulting from the accumulation 
of excessively fine calcareous mud (e.g., Fuller's Earth Rock and 
some beds of Great Oolite Limestone). By the coming in of 
shell fragments and oolitic grains the compact type passes into 
the shelly or oolitic type. In fact no hard and fast line can be 
drawn between the different rocks. 
The shelly limestones consist mainly of shell- fragments, and 
the oolitic limestones of spherical or ellipsoidal grains of cal- 
careous matter the so-called oolitic grains. The matrix in 
which the shell-fragments or oolitic grains are embedded, may 
consist of fine-grained calcareous mud similar to that of which 
the compact limestones are mainly composed, or of clear crystal- 
line calcite, or of mixtures of these substances. The shelly and 
oolitic types are of course connected together by intermediate 
varieties. In a few cases there is no matrix at all ; the oolitic 
grains having been- merely soldered together at their points of 
contact by minute crystals of calcite (e.g., Inferior Oolite free- 
stones of Weldon and Stamford). 
There is a variable amount of what may be termed ordinary non- 
calcareous detrital material, the nature of which is best studied by 
