Old Red Clay Bricks

After a few weeks of continuous wet weather we resumed our dig at Rouse Hill Anglican College and discovered these pieces of Red Brick. They are very old, include numbering marks N23 on one and 6 or 9 on the other. They are quite thick, show that there were holes in the centre, and seem to have been glazed (matte) finished as some point. We suspect that they are pre-1950's.
Here's some interesting info on brick history in Australia:
http://www.dictionaryofsydney.org/entry/bricks
http://www.migrationheritage.nsw.gov.au/exhibition/objectsthroughtime/convict-sandstock-bricks/