Varying greatly in thickness, coal seams run at various angles and depths in relation to the surface. These factors condition the choice of mining operation. The "drift mine" is employed in situations where one can enter the coal seam directly on a horizontal or upward plane. There are few such mines in Nova Scotia, although the earliest cuttings by the French were made directly into the sea cliffs near Port Morien. More common in Cape Breton, the "slope mine" penetrates the seam either at or near the surface and coal is brought up along an inclined plane, usually at less than forty-five degrees. Where the coal does not crop close to the surface or where the nature of the seam makes exploration of the deeper portion more economical, a "shaft mine" is dug. This latter type is more frequently the case in Pictou County.
Another mining technique, never widely used in Nova Scotia, is the "strip mine" so-called because the overburden is stripped away and the coal removed directly. This technique is only possible where coal seams lie very close to the surface, and it is only economical when the seam is relatively thick. Although the most economical method of mining, it also results in the greatest environmental damage.
Nova Scotia's coal seams generally lie deep below the surface and overlay one another at various levels. Proximity to the coastline often results in the greater part of the seams lying under the ocean floor. Variations of thickness and pitch can be determining factors for the economic viability of a particular mine or seam, and a great deal of expensive exploration has always been a prerequisite for investment in extensive workings on the surface. The large number of companies which lost everything in a gamble on an unproven seam is testimony to the folly of investment without adequate exploration.
