Looking for 1950's Era YA(?) Time Travel Novel Involving Traveling Back to the Stone Age

[Kenneth G. Holloway]

There is a novel I am trying to find but I can't remember the title or author. The plot was about a teenager who was accidentally transported to the Stone Age when an earthquake activated a time machine his Father or Uncle was building to travel back to ancient Rome. It must have been published post 1945 because the time machine was constructed by a scientist / engineer working at Alamogordo and was atomic powered. Most of the story followed the teenager as he explored the stone age landscape and learned to live with a local tribe. One scene that sticks in my mind is when the main character decides to "prank" future archeologists by painting a rock with the inscription "E=MC2" and burying in a cave next to the stone age tribe's drawings of prehistoric animals. Any help would be appreciated.

 

[CassFrank]

Perhaps Mists of Dawn by Chad Oliver?
Reader reviews

 

[CassFrank]

To add: the summary here describes cave painting.

 

[BAYLOR]

Perhaps Mists of Dawn by Chad Oliver?
Reader reviews

ive never seen him in print. Sounds interesting;