Does microevolution logically include macroevolution?

I can't see any inherent contradiction in the view that organisms exist in what are, essentially, viable islands in the sea of possible genomes. So that a cat, for example, could evolve to be bigger, smaller, more aggressive or blacker but not evolve into an aquatic mammal akin to a seal because there exists no gradual pathway between the two possible organisms.Of course the evidence contradicts this view; but I can't see any logical reason it couldn't be that way.

The view that the existing lifeforms exist in seperated pools of viability with the posible genomes. I.e. that there is no possible pass path between an animal and a very different sort of animal (clearly we're not talking about a cat evolving into a seal, 'cos that isn't what evolution proposses, but that a cat could evolve into something like a seal).The evidence overwhelming supports a strong evolutionary position that all life on earth evolved from a tiny number of common ancestors (probably, but not yet certainly, one) and, in particular, that all birds, mammals, reptiles and amphibians share a common ancestor.

Depends on what you mean by that. Given time anything can evolve to fit pretty much any niche (assuming the right conditions/competition/etc.) but an aquatic filter feeder evolved from a penguin is not going to be a whale. I dislike the terms micro and macro evolution they're too sloppily defined. But yes, I'd say it does. But that's not the same thing as saying it must; which is why proving the occurance of microevolution is not enough to demonstrate the whole theory of evolution.