Commerce power in late 19th and early 20th century

[Earl Maltz]

	While I was observing a class being conducted by one of my colleagues, he 
stated (twice) that, during the late nineteenth or early twentieth century 
the Court held that Congress had authority to regulate working conditions 
in mines and quarries under the Commerce Clause.  I don't know the case to 
which she was referring (although the Court did hold that the state of Utah 
had such authority in Holden v. Hardy).  Indeed, my understanding is that 
the case law of that period was to the contrary.  Is my understanding of 
the law wrong?  Can anyone point me to the case to which my colleague was 
referring?

	Off list responses are fine.