Again, the most convenient site for oil wells is the crest of an anticline or "dome," where an impervious stratum imprisons the gas and oil in a subjacent saturated layer under pressure.
Of England are the two Tertiary basins of London and Hampshire, separated by the dissected anticline of the Weald.
Where they dip away from the axis of movement the structure is termed an anticline or anticlinal fold; where they dip towards the axis, it is a syncline or synclinal fold.
The principal structural feature is the broad anticline, its axis running north and south, which has brought up the Carboniferous Limestone; this uplifted region is the southern extremity of the Pennine Range.
On the south side of a well-marked anticline in the Upper Old Red Sandstone at North Sannox, the Carboniferous strata reappear on the coast with a south dip showing a similar ascending sequence for about half a mile.