"Never will a daredevil succeed in being champion of cyclocross!" - Eugène ChristopheI just came across these images on blackbirdsf.org (via Mr CrossTube). The top composite shot is from Le Cross Cyclo-pédestre des Mureaux, November 1921, the second shot of the steep bomb hole (I'd look at that twice on an MTB, let alone a pre-war road bike!) is from the 8e Critérium International de Cross Cyclo-pédestre, 07 February 1932, and finally, the last shot is from Prix Pasbecq, 11 Jan 1931.
The cyclocross archive on blackbirds.org is very cool, I urge you to go and have a look!