UPDATE: I've had a look on the net and I think it may well be a rough coated Scotch Collie which was the working forerunner of the handsome but pretty damn useless breed standard rough collie (Lassie). The boy's kilt would indicate that I may be right although it is a breed that has survived in the USA with far more tenacity than it has in the UK, even Scotland.
I wonder what breed of collie that is. It has the coat of a rough collie but the nose is not narrow enough. My guess it is from one of the many breeds of collie that are no longer around although their DNA lives on in modern, more standardised breeds such as the border collie. Whatever, it's a very beautiful dog indeed and the terrier (Cairn?) in the cart looks like he's a right character as well.