Microscopic Journal, and Structural Record . m the gyyot to the xtt^ ^^ *^inch. The spicula are large in proportion to the other parts of the tissue, very frequently exceeding the eighth or tenth of an inch in length. They are thinly scattered, and usually acicular in their form ; but sometimes they are forked or branched, but this is comparatively a rare character. They do not occur in fasciculi, as in Halkhondria, but are usually solitary, or a few are grouped together. They are mostly of an elongated, spindle-formed shape and somewhat curved, as represented in fig. 1, which exhibits them in
Microscopic Journal, and Structural Record . m the gyyot to the xtt^ ^^ *^inch. The spicula are large in proportion to the other parts of the tissue, very frequently exceeding the eighth or tenth of an inch in length. They are thinly scattered, and usually acicular in their form ; but sometimes they are forked or branched, but this is comparatively a rare character. They do not occur in fasciculi, as in Halkhondria, but are usually solitary, or a few are grouped together. They are mostly of an elongated, spindle-formed shape and somewhat curved, as represented in fig. 1, which exhibits them in their natural position, on the interior surface of a flint from Wiltshire; or in fig. 2, which gives a series of the largest of them, separated from the white friable siUcious matter from the interior of one of the Wiltshire flints. The results arising from the examination of the flinty bodies of the chalk, induced me to believe that the cherts of the greensand forma-tions and of the oolites, would probably prove to be of a similar 134 ON THE SILICIOUS BODIES OF CHALK, ETC. I therefore examined thin slices of specimens of chert from the uppergreensand pits of Fovant in Wiltshire, in the manner pursued in theinvestigation of the flints ; and I found, as I expected, the result to beof a similar description ; but in this substance the spongeous fibre isof a much coarser texture than in that of the chalk-flint, and the inter-stices of the net-work very much larger in proportion. The imbeddedextraneous matters are also of a larger description, such as small frag-ments of apparently very fine branched vegetables, &c,, in addition toXanthidia and other small organic bodies. The form and mode of ra-mification of the tubular structure approaches nearer to those of thefibre of the common Mediterranean sponge, than in the flint tubes are seen dispersed in about an equal proportion through thewhole mass of the chert. Theyare very pellucid, and would probably escapeob
Size: 1307px × 1912px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, bookpublisherlondon, bookyear184
