Shipton leaned to his right and began to chip away at a large outcrop of ice directly above Dean, laughing as a loosened piece tumbled downward, striking Dean's exposed head, nearly knocking him senseless.
The difference in level between the outcrop of the assumed eastern intake and of the wells is often so small, in comparison with their distance apart, that the friction would completely sop up the whole of the available hydrostatic head.
It should be noted that the oxidation of sulphur itself by atmospheric influence may give rise to sulphuric acid, which in the presence of limestone will form gypsum: thus the sulphur-deposits of Sicily suffer alteration of this kind, and have their outcrop marked by a pale earthy gypseous rock called briscale.
Fragments of coal, or soil stained black with coal, will be found near the outcrop tif coal beds.
By tracing such indications up the stream or up the hillside the outcrop may sometimes be found, or at least approximately located.
The outcrop of a metalliferous vein frequently manifests itself as a line of rocks stained with oxide of iron, often honeycombed and porous, the " gossan " or " eisen-hut," the iron oxide of which results from the decomposition of the pyrites, usually present as a constituent of such veins.
By sinking additional pits or by extending the costeaning trenches and uncovering the outcrop of the deposit more fully it is sometimes possible to obtain all the information required for the most extensive and important mining operations.
Even when the outcrop is oxidized, and Surface the mineral character and richness of the deposit is Explora- altered thereby, it is possible to determine variations tion.
In thickness and the extent and distribution of the rich and barren areas by outcrop measurements.
If the deposit shows great variations in thickness in its outcrop along the surface it is probable that a drift or a slope would show the same thing in depth.
If the workable areas are poor, and appear only at long intervals along the outcrop, the chances of discovering richer areas by a shaft are very small.
For example, the deposit does not outcrop as in the case of blind.
Veins and flat deposits below the general level Boring of the country; or the outcrop lies beyond the limits of the property or under water or water-bearing formations, or is covered by quicksand, or is deeply buried.
The outcrop ploration.
Below the oxidized outcrop the vein is often increased in value by secondary enrichment, sometimes to a depth of several hundred feet.
A drift or entry is a horizontal passageway starting from the outcrop and following the deposit.
If the outcrop of the vein or bed is accessible the shaft may be inclined and sunk to follow the deposit.
In the early days of coal-mining, open working, or quarrying from the outcrop of the seams, was practised to a considerable extent; but there are now few if any places in England where this can be done.
In mines that are worked from the outcrop by adits or day levels traction by locomotives driven by steam, compressed air or electricity is used to some extent.
The Black Reef series of quartzites and conglomerates and dolomite form a narrow outcrop resting unconformably upon the last-mentioned system.
The Thanet beds resting on chalk form a narrow outcrop rising into cliffs at Pegwell Bay and Reculver, and consist (1) of a constant base bed of clayey greenish sand, seldom more than 5 ft.
Such a change is very common on the outcrop of mineral veins, forming what miners call "gozzan."
To the south-east of this region a narrow outcrop of Upper Llandovery, Wenlock and Ludlow sandstones and mudstones follows, uncomformably overlying the Llandeilo and Bala rocks, and dipping conformably under the Old Red Sandstone; they extend from Newbridge-on-Wye and Builth through Llangammarch (where there are mineral springs) towards Llandovery, while a tongue of Ludlow rocks brought up by faulting extends from Erwood on the Wye for 8 m.
Beneath this Chul formation the older beds of the outer and Turkestan ranges dip and pass to an irregular outcrop near the banks of the Oxus.
The table on p. 660 contains the names that have been applied to the subdivisions of the Cambrian strata in the areas of outcrop in Wales and England; at the same time it indicates approximately their relative position in the system.
The regular form of the Himalaya, constituting an arc of a true circle, appears to indicate that the whole chain has been pushed forward as one mass upon a gigantic thrust-plane; but, if so, the dip of the plane must be low, for a line drawn along the southern foot of the Himalaya would coincide with the outcrop of a plane inclined to the surface at an angle of about 14°.