Volcanic rocks, locally called "Toadstone," are represented in the limestones by intrusive sills and flows of dolerite and by necks of agglomerate, notably near Tideswell, Millersdale and Matlock.
A few hornblendeschists are metamorphosed gabbros; others have developed from dikes or sills of lamprophyre.
The chief portion of this rig is the derrick, Oil which consists of four strong uprights or legs held in Derrick position by ties and braces, and resting on strong wooden sills, which are preferred, as a foundation, to masonry.
The depth of water on the dock sills varies from 172 ft.
The Mediterranean Sea also belongs to this group; its various deep basins are homothermic (at the winter surface temperature) below the level of their respective sills - the Balearic Basin below 190 fathoms at 55° F.; the Eastern Basin below 270 fathoms at 55.9° F; the Ionian Sea at 56.3° F.; and at 56.7° south of Cyprus.
They are dark blue-grey, fine grained and durable, and are much used for flagging and kerbing and for sills, caps and steps.
On the sills, and are open to Canadian and American vessels on equal terms; the equipment is in every respect of the most modern character.
Immense -sheets of dolerite, gabbro, or allied basic rocks indicate eruptive materials intruded as sills or poured out as lavas contemporaneously with the sedimentary formations among which they lie.
In the south of the island there are sills and dykes of felsite, quartz-porphyry, rhyolite, trachyte and pitchstone.
The best example of the basic sills forms the Clauchland Hills and runs out to sea at Clauchland Point.