The tunnel was dug mostly through compacted sand with some thin strata of hard rock in between, making light blasting necessary.

Our bow side entry screens were flaming white hot from atmospheric friction in spite of our passage through the thinnest upper strata.

Thus it developed that my flagship soon raced through the thin upper strata looking like a red-glowing sunball.

Hence the statistical properties of the population may not be preserved if there are thin strata.

These thin strata, close to the surface, were extracted through open cut workings, which were then smelted by the monks in small bloomeries (early furnaces).

But what this meant in reality was recruiting a thin stratum of educated and loyal workers and removing them from the factory floor.

Local trade grew perceptibly and a thin stratum of relatively well-off artisans and merchants began to emerge.

As a result only a thin stratum of wealthy native merchants developed.

The glacial till is generally decalcified to 3-4 metres; thinner strata may be entirely decalcified.

Most of the surface consists of thin strata of hardened clay with pockets of water between them.