890 Opinions upon Clay Stones and Concretions, [ ote 
gtl. That the concretions vary in specific gravity: Pa 
2.49, 2.54, 3.34; the writer, 2.60, 2.57, 2.67, 2. 59. 
1oth, That many show periods of growth (PI. XXVI, Figs 4, 
Pl. xxvu, Fig. 5). 
Further, the results of microscopic examination tae 
these: A horizontal, equatorial section of an oblate concre- 
tion, when examined with an one-eighth objective, showed an 
densely crowded with crystalline points of calcite, so í 
packed as to resemble a patchwork of fine mosaic, of which t 
separate pieces varied in apparent size from 1% to ⁄™™ 
was seen in polarized light. No apparent variation in their nu 
ber between the center and circumference of the disk was n 
but there were evident crowds or congeries of these s 
specks in places, though usually their distribution was uniform. 
Between crossed Nichols irregular and loosely connected dark 
blotches or clouds appeared over the field between which, int 
lacune, shone transparent plates of calcite varying in size. Black 
lines in labyrinthine reticulations seemed to outline the cal 
crystals, the latter lying in their meshes. a 
A cross vertical section revealed no linear arrangement 
calcite crystals, and in the slide in question the minute ~~ 
of the horizontal section was repeated upon a possibly dense 
more microscopic scale, whilst between crossed Nichols thes 
loops and blotches of clay became very noticeable. 
A horizontal section through a group of three concr 
showed the subjoined outan ae 
lane surface was ground tor ee 
din to the glass, the outlines oi te : 
side concretions being very faint. 
The section presented, under the microscope, no opeet y 
tures from those examined before, unless the groupings °°" 
specks were slightly more marked. The clay lines 
larger and more meshy, like a net. On removing 
with hydrochloric acid the clay remaining on the slice | 
a surface of perforations. The apertures varied in ca re 
the comparative size of the calcite crystals ge up i 
though many such openings were previously the remove 
packed calcite lenses. Sometimes the holes left by ike a bY” 
calcite were inclined tubes, and the fenestration thoai 
zoan surface, The acid washed on the thin film ; 
