Stop+4+Cross+Bedding

CROSS BEDDING
Locate the northeastern corner of Sir Howard Douglas Hall (labelled Kings College) (this is the corner closest to the Lady Beaverbrook Gymnasium). At about eye level above the basement level windows is a band of rock that sticks out from the walls of the building by an inch or so. Count six blocks along the longest wall of the building towards the main entrance. This block contains some brownish curvy lines - this is called cross bedding - but dont worry, it's not cross at you, he he.

This is the oldest university building continuously in use in Canada.

The stones are all locally excavated. These are sandstones: sand sized particles that have been compacted, and naturally cemented into rock. They were all deposited about 300 million years ago in ancient rivers that flowed across this region. The bottoms of the rivers were not always perfectly flat, as is also the case in rivers existing today. The curved lines you see in the rock are caused by a water current depositing lens like layers of sediment on a slight depression in the river bed, as shown to the right. These are called ‘cross beds’

We can determine the direction of water flow, and sediment transport, by looking at the geometry of the cross beds (see below). The cross beds always slope down in the direction of sediment/water transport (unless the stonemason turned the rock upside down when he laid it, which is another story entirely!)


 * EXERCISE:** Assuming the beds in the wall were not inverted by the stonemason, (i.e., they are the same way up in the building as they were when they were in the ground) was the ancient water current moving towards the west (right) or the east (left)?