Dan Mitchell wrote:
"Hog fuel” however is a bit more than the modern term “wood chips” would imply. The term can include large chunks, up to what we now call cordwood. The larger pieces were commonly used to fuel donkey-engine winches and such in the woods. Cars dedicated to such large-chunk service were also sometimes called “block cars”, a term which can have different meanings in other contexts.
Can't speak for other railroads, but on the SP and NWP, a "block car" was for shipping the blocks that were later split into shingles or shakes.
Tony Thompson Editor, Signature Press, Berkeley, CA
Publishers of books on railroad history