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This may be inferred from their manner of development in the individual, as well as from a long and perfect series of gradations in different species and genera, from simple granules to ordinary spines, to perfect tridactyle pedicellariae. The gradation extends even to the manner in which ordinary spines and the pedicellariae, with their supporting calcareous rods, are articulated to the shell.
The bed above the junction was narrow but deep, and the permanent character of its banks gave to this channel the appearance of a considerable tributary, which it probably may be at some seasons, although then dry. In a section of the bank near the junction, I observed a bed of calcareous tuff. The passage of this channel was easiest for the carts at the spot where it joined that of the Gwydir.
I have found an abundance of tuf, and also of goitrous persons in Derbyshire, the Valois, the Valteline, at Lucerne, Berne, Fribourg, in parts of Piedmont, in the valleys of Savoy, at Milan, and at Dresden. I also observed that at Berne and Fribourg, the public fountains are supplied from sources where there is a vast quantity of this calcareous deposit.
Had M. Schreiber found any pieces of the vein contained in the calcareous rock, he would have had good reason for that assertion; but, to conclude that fact from grounds which do not necessarily imply it, is not to be permitted in sound reasoning, if certainty is the object, and not mere probability. SECT. II. The Theory confirmed from Observations made on purpose to elucidate the subject.
Before we leave the plains of Cumana, and the breccia, or calcareous sandstone, which constitutes the soil of the seaside, we will describe the different strata of which this very recent formation is composed, as we observed it on the back of the hills that surround the castle of San Antonio.
He suggests that the Ventriculites of the chalk were nearly allied to these sponges, and that when the silica of their spicules was removed, and was dissolved out of the calcareous matrix, it set into flint. The occurrence here and there, in the white chalk of the south of England, of isolated pebbles of quartz and green schist has justly excited much wonder.
The hardly less startling hypothesis that the Echinoderms are coalesced worms, on the other hand, appears to be open to serious objection. As a matter of anatomy, it does not seem to me to correspond with fact; for there is no worm with a calcareous skeleton, nor any which has a band-like ventral nerve, superficial to which lies an ambulacral vessel.
In Lombardy, between Vicenza and Albano, where the calcareous stone of the Jura contains great masses of basalt, I have seen the latter enter into effervescence with the acids wherever it touches the calcareous rock.
He ascertained by dredging that living testacea were there grouped together in precisely the same manner as were their fossil analogues in the inland strata; and while some of the recent shells of the Adriatic were becoming incrusted with calcareous rock, be observed that others had been newly buried in sand and clay, precisely as fossil shells occur in the Subapennine hills.
The earthquakes and subterraneous detonations of which the seat has been erroneously sought in the calcareous mountains of Cumana have been felt with most violence in the granitic soils of Caracas and the Orinoco.
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