One of the main concerns facing coal-mine operaters in the Estevan-Bienfait area is the undulating nature (small anticlines and synclines, Fig. 44) of coal seams as well as theirdisruption caused by fault displacement. In some coal mines, the fault contact is essentially vertical between Ravenscrag siltstone and coal, on the one hand, and dense clay till, on the other (see Fig. 45, snapshot of the vertical contact taken from an oblique angle). As a consequence of such displacement, it is necessary to define the geometry of separated and missing sections of coal beds (Fig. 46).

Seepage along coal-mine joint fractures (Fig. 47) is a lesser concern than folding and faulting of coal seams. An additional feature in coal mining is the widespread occurrence of old underground coal mines, many dating back to the early 1900s. During overburden excavation, using huge 80-ton capacity draglines, a machine operator might suddenly happen upon an old coal mine tunnel (Fig. 48). These tunnels are small in diameter, and do not present a concern since they can usually be avoided in mining.

A decade or less ago a small unattended child wandered into the adit of an abandoned mine near Estevan. The child was not able to get out and died from lack of oxygen. As a consequence, the provincial government undertook an extensive airphoto survey to locate all abandoned coal mine workings in the area. Following their location, the tunnel entrances were plugged.

The Shand access road, over which we travel,passes directly over the corner of a long abandoned underground coal mine (Fig. 49). Aligned dots on aerial photographs mark the location of collapse-depressions over abandoned coal mine tunnels (Fig. 50). Many of the cave-indepressions are visible from the road.

After viewing active mine workings and piles of strip mine waste material, we will visit an area of reclaimed mine waste, which has been levelled, blanketed with what is referred to as 'cover' soil (rather than topsoil), seeded to a mixture of alfalfa and rye, fertilized, and leased to nearby farmers for hay land. Old waste piles south of Estevan are often dotted with tall trees. The piles of waste spoil have not been disturbed because,over time, a whole new ecosystem has developed on them.

We'll head back to Regina now, and to the ice-breaker reception. En route back to the city--perhaps in fall darkness--we will pass, at some distance, an extraordinary landscape that consists of whole townships of light-

toned ring features (Fig. 51). The 'rings' are more or less nested together, equally spaced, and much the same size. The question arises: What is their likely origin?

Q Figs. 45, 46 - Inspecting a coal mine south of Estevan a few years ago, one could observe a possible 10-m-high vertical contact between Quaternary dense clay till a few tens to hundreds of thousand years old and Tertiary Ravenscrag Formation clastic strata 57.8 to 66.4 million years old-and without any apparent mixing of the two different materials along the vertical contact. Can you explain the geological processes and environment that may have created the vertical contact?

Q. Fig. 51 - There are at least four (4) explanations for the origin of 'rings' in the landscape appearing in Fig. 51. As indicated, the rings are all much the same size, are more or less equally spaced, and surround slight saucer-shaped depressions. Can you name the four explanations? What significance does the ring pattern have in highway construction and in dam site construction?