We have no meanings for "worked at intervals" in our records yet.
The mines have been worked at intervals since, and as late as 1845 a smelting-house was built in the valley.
At this portrait the unsatisfied painter worked at intervals for four years, and when he left it he pronounced it still unfinished.
For a whole week he worked at intervals, building his chimney with stones from the river bed, and laying them well and truly.
It has been worked at intervals for upwards of two centuries; but, being now less productive, the ore has been excavated for several years consecutively.
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