This team of scientists, known as geologists, has been spending its time digging deep holes around London to find out exactly what the earth under our feet is like.

It has even dug some holes under the River Thames!

We've got some pictures of their work (see downloads, right).

Using powerful drilling machines called boring rigs, the team has been able to dig down 60 metres below ground.

They’ve found some amazing things, including soil deposits that date back 65 million years to when dinosaurs roamed the earth!

The soil from these digs is transported to laboratories where the geologists run a series of tests to find out exactly what the soil is like.

For example, lots of London soil is heavy clay that is very good for drilling tunnels through.

Other soil is more chalky, which means that careful measures need to be taken when drilling through it.

This information is very important in helping Crossrail to find out where, and how, it should build its tunnels and stations.

No construction work will be able to begin until the geologists have investigated every part of the Crossrail route – and who knows what further secrets they may find in the meantime?