Well, all I can say is that this is a member of the Fabaceae (Leguminosae) and it could be one of your Wattles (Acacia). They look like seedlings and those pinnate leaves are normally the juvenile phase (for Australian species) and are lost as they become older, ending up looking more like Eucalyptus with modifies leaf stalks expanded into Phyllodes. The juvenile pinnate leaf phase is normally lost completely after several years.

As to the species..................................go on, you guess :-)

Ha ha... thanks Fractal for all that handy info.
It grows VERY, VERY, VERY fast: I used to have one just round to corner from our house. Some of my earliest memories include running around it (it would only have been 2 metres tall then).
When I was about 5 or 6 I remember climbing it and hardly being able to get onto the bottom branch because it was so tall.
Then just last year (when I was 12) I noticed it again and it was 10+ metres tall...I couldn't even recognise it as the same tree!!!!!
And this year it was so tall the Council had to cut it down - so ends a very short, quick-growing lifespan. It's the fastest grower I know.

Does this help?

Yes, sounds like Blackwood, Acacia melanoxylon. Wonderful species!

It looks like acacia dealbata to me. I walked underneath one at my daughters school this morning and it was identical. The Dealbata Acacias are very fast growing.

Thanks Andrea, it is Acacia dealbata. ( I just googled it)

:o)))))))

Just one more point, does or did the trees ever produce a mixture of juvenile and adult foliage like this?

http://www.rcplondon.ac.uk/garden/2007-07/Acacia%20melanoxylon%20-old%20and%20new%20leaves.jpg

If they only produced the divided foliage, then it may well be as Andrea says.

I don't know Fractal, I've only ever seen the divided foliage like in the pic above

Acacia melanoxylon!! Thanks fractal, I have this being a simbiant on a tree fern and the leaves are just like this. I thought it was Acacia longifolia, but the juvenile leaves really stumped me. I have been looking for ages, great!!

No problem Andrea. Looks like Pip c's plant is A. dealbata.

Thanks all for your helpful comments! :o))))