It has been conjectured that this carbonaceous matter may be due in great measure to large quantities of imbedded animal remains, for the number of Graptolites included in these slates was certainly very great.
In Great Britain eleven genera and about 40 species of Graptolites occur in the Llandeilo flags and underlying Arenig beds.
Some graptolites were straight, and some curved or spiral; some were single stemmed, and others consisted of several radial stems united.
Fishes were as yet few and small; trilobites and graptolites had now passed their prime and had diminished greatly in numbers.
Graptolites occur but rarely in the Upper Cambrian.
These Graptolites are specially characteristic of the Upper Cambrian and Lower Silurian.
The range of the Graptolites in time extends from the Cambrian to the Carboniferous.
Fucoides dentatus and serra of Brongniart, from Quebec--are graptolites of two species quite common there.
He found that the species of graptolites have each a comparatively narrow vertical range, and they may consequently be used for stratigraphical purposes.
In the Silurian system, for example, the graptolites have been shown by C.
Applying the method, in the first instance, to the highly plicated Silurian rocks of the south of Scotland, he found that by means of graptolites he was able to work out the structure of the ground.
Lastly, there is a group of Graptolites (Phyllograptus, fig.
If the Graptolites belong to certain genera, we may be quite certain that we are dealing with Lower Silurian rocks.
All the branching and complex forms of the Arenig, the twin-Graptolites and Dicranograpti of the Llandeilo, and the double-celled Diplograpti and Climacograpti of the Bala group, have now disappeared.
The Graptolites are usually found in dark-coloured, often black shales, which sometimes contain so much carbon as to become "anthracitic.
In another great group of Graptolites (including the genera Diplograptus, Dicranograptus, Climacograptus, &c.
Graptolites were slender, plumelike, delicate forms consisting of colonies of tiny individuals, in many cases in branching or radiating combinations.
The abundance of graptolites in black shales associated with few other organisms has often been noted.
The trilobites and graptolites still contribute largely to the fauna, the latter becoming very scarce at the summit of the system, though a few specimens have been detected in the rocks of the succeeding system.
Footnote 78: The importance of the graptolites as indices of the geological age will be seen by perusal of Prof.
Of extinct groups, the graptolites and trilobites seem to have been entirely confined to the sea.
The graptolitesof the black shales are Upper Llandeilo forms, but the thin deposit of radiolarian chert may represent the rest of the Llandeilo period and part of the Arenig period also.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "graptolites" in a variety of sentences. We hope that you will now be able to make sentences using this word.
