What is this mix I keep seeing?

I see a lot of them too.
 
[linkhttp://wwww.petfinder.com/fotos/KS107/KS107.6812539-1-x.jpg]http://wwww.petfinder.com/fotos/KS107/KS107.6812539-1-x.jpg[/link]
 
Often here they are labeled lab/border collie or lab/australian shepherd.  I have no clue if either of those might be right.

Yeah, I know what you're talking about.  They're everywhere, aren't they?  From what I've read, small amounts of white are permissible in AKC Labs.  Perhaps if the breeding isn't watched closely, it can spread.  Here's the site for a kennel that breeds Labradors, from what I've heard, it's a fairly nice kennel.  [linkhttp://www.woodhavenlabs.com/mismarks2.html]http://www.woodhavenlabs.com/mismarks2.html[/link].  They show some white marked Labs. 

Maybe a Dalmatian/Black Lab mix? Ive seen alot of those mixes and theyve all had the same with feet and white chest sometimes with a bit of spotting in the white areas.
 
 

pit bulls also come in black and whit and contribute to those mixes  but the thing I wonder about is how many of those lab mixes actually have lab in them any black dog is labeled Lab mix bu there are lots of black dogs

Labs, left to their own devices, tend to breed readily with others, which is why the assumption is made so frequently.  The likely scenario, if you are visiting shelters in the Northeast, is that the dogs are Pit/Lab mixes, or Pit/something else mixes.  If the dog is short-coated, then both parents were probably short coated, since long hair is a dominant characteristic.

Fuzzdomestic that's very interesting. I suppose more are purebred than I thought...

Spiritdogs, I don't live in the northeast, I live in central VA. We do have a fair amount of pit bulls though. I can usually tell when a dog is a pit mix though because they have wider heads (but yes I know not every mix that has a wide head is a pit mix, many are boxer mixes and other mixes...) Here the three main dog breeds in shelters are labs, various hounds (and pointers to a lesser extent), and pit bulls.

Can hounds produce the white markings when mixed with a black lab or other black dog?

There are lots of dogs who could have similar markings.  Cocker Spaniels, Border Collies, Australian Shepards, Pit Bulls, Labs, Italian Greyhounds.  I saw a chihuahuha/Jack Russel with those markings.  It could be any number of those dogs, or any other kind of dog that I haven't mentioned.  Most likely, it is just a huge cross of breeds.

Short hair is dominant over long. Terrier (or bearded) coat is dominant over both those. Thus, if there's a high percentage of labs, hounds, bully breds, short haired BCs, smooth coated Jacks, boxers, Dals, etc in a random breeding population you'll see a lot of lab type coats.

"Irish" markings (the white trim) are carried by almost every breed, no matter what the standard says. It's a recessive characteristic, which means you can breed for "no white trim" for thousands of generations and still have it pop out if the right dogs get together. Obviously, in a random gene pool you'll see it more for that reason, since many individual dogs are homozygous for the characteristic. Hunting hounds, for instance, carry it, and since ear set goes UP in carriage and DOWN in size in random populations, it's possible the nice little labby looking dog with white trim is something mixed with anything from a beagle to a fiest, and on up to a Walker treeing hound.

Our lab/beagle mix, Shadow, has white on her chest and the very ends of her toes, a little on the belly and the tip of her tail.

Sounds like my Clyde! If the breed you are speaking about looks like my profile pic it is definitely a Border Collie/ lab mix. Mine has a little but of husky as well but it doesn't show in him. Hope that helps!
~Nicci