When this metal exists in the bosom of primitive rocks, it is particularly in schists; it is not found in serpentine, but it is met with in greywacke in Transylvania.
Judged by mere vertical depth, they present but a meagre representative of the massive Devonian greywacke and limestone of Germany, or of the Old Red Sandstone of Britain.
The following is his description of the rocks, slightly condensed:—Greywacke passing into greywacke slate, greywacke with small imbedded crystals of hornblende, dark greenish or blackish grey clay slate.
Section across Greywacke area of Oxnam Water; G, Greywacke and Shale; C, Sandstone, etc.
The continuous lines between A and B represent thegreywacke beds as we now see them in section; the dotted lines above A A indicate the former extension of the strata, and the dotted lines below B B their continuation below that datum line.
Although the bottom rocks of the Cheviot Hills are thus apparently separated from the great greywacke area, there can be no doubt that they are really connected with it, the connection being obscured by the overlying younger strata.
The succession of rocks at Allars Mill is seen in many other places in the Cheviot district, but enough has been said to prove that the greywacke beds are the older of the two sets of strata.
No longer cooped up in the rocky gully, painfully worn for itself in the hard greywacke and shales, the stream now winds through a much deeper and broader channel which has evidently been excavated with greater ease.
These ridges are the exposed edges of beds of greywacke and shale, which are here standing on end.
Again, when we trace out the boundaries of any detached areas of greywacke we invariably find these bottom beds disappearing on all sides underneath the younger strata by which they are surrounded.
At present, however, we are only concerned with the relation which these bear to the greywacke and the red sandy beds.
There is another class of rocks, the relative position of which we must now ascertain, for no one shall wander much or far among the Cheviots without becoming aware of the existence of other kinds of rock than greywacke and sandstone.
A stone ring, made from the ordinary greywacke shale of the district; it was too small for the finger.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "greywacke" in a variety of sentences. We hope that you will now be able to make sentences using this word.
