174. A. R. Horwood—Aragonite in Middle Lias, Leicestershire. 
form, apart from the part it plays in the formation of shell-layers at 
that horizon, is assuredly of interest. Hitherto the Liassic strata have 
not yielded any minerals unassociated with shell-structure, except 
selenite, which occurs commonly in some Upper Liassic clays, whilst 
it is not unusual to find fossils converted into iron-pyrites or marcasite, 
especially at certain horizons. The Doggers of Yorkshire are note- 
worthy instances of this kind. In the Middle Lias, zine, nickel, and 
cobalt are found in the iron-ores of the Cleveland district.! 
Whilst confined hitherto, so far as I am aware, to the parts of 
shells, ete., which have not been converted into calcite—the usual 
form taken by carbonate of lime when replacing the lime secretions 
of shells of Mollusca and other testaceous animals—aragonite has now 
been discovered by the writer unassociated with organic remains in 
the Amaltheus spinatus beds of the Middle Lias, or Rock-bed, at 
Tilton Hill, near Lowesby Station, Leicestershire. 
The mineral exhibits clearly the acute pyramids characteristic of it, 
with orthorhombic crystals. Although not common it forms a mass 
about a foot square in some places the crystals being radially arranged, 
as is usually the case, with their terminations all directed to a common 
centre, in much the same way as those of quartz in the ‘ potato- 
stones’ or geodes of the Trias. But their mode of occurrence seems 
best compared with certain boulders of strontia, discovered by Mr. H. 
Bolton” at Leigh Court, near Bristol, the outer surface presenting an 
amorphous rounded exterior, characteristic of worn boulders in 
general. 
The surface of the Tilton boulders does not, like the Triassic 
boulders, present grooves. I was informed by Mr. G. W. Lamplugh 
that the Middle Lias at Barnstone presents strie, but these are 
probably not of Marlstone age, but truly Glacial (or post-Pleistocene). 
It is interesting to note that in typical aragonite a small percentage of 
strontia (4 per cent.) usually occurs. The exact horizon of these 
deposits at Tilton Hill is a few feet at most, usually a few inches, 
above the thick ‘‘encrinital limestone band’’, which occupies so 
constant a position, just below the Transition- bed, between the 
Middle Lias (spinatus-beds) and the Upper Lias. This horizon is 
a well-marked one, and may be traced all over the higher ground at 
Tilton Hill. The name ‘ encrinital limestone band’’,? adopted from 
Wilson,* is not quite correct, since encrinites do not enter into its 
composition, but, as pointed out elsewhere,*® this band is made up of 
joints and portions of stems of Crinoids, with fragments of Pecten, 
Polyzoa, and other littoral organisms, resembling in composition 
some forest marbles of the Eastern Counties, as suggested to me by 
Professor T. R. Jones. Perhaps a better name, more correct from 
a paleontological point of view, is erinoidal limestone band. The 
crinoid stems, though fragmentary, are abundant, and the horizon 
1 Vide Rudler, ‘‘ Minerals of the British Isles’’: Mem. Geol. Sury., 1905, p. 191. 
2 See Grou. Mac. , 1907, p. 471. These boulders varied in Bie: from. that of 
a pea to that of a mass 100 tons in weight. 
5 Grout. Mac., 1907, pp. 462-3. 
4 Tbid., 1886, p. 296 et seqq. 
5 Trans. Northants Nat. Hist. Soc., 1907, p. 105. 
