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Oddly enough (or maybe not, because I am a geologist) I have handled both the Green River Shale near Parachute Creek and the Bakken in core samples. The Bakken isn't quite dry to the touch, but nearly so. In core it looks like roofer's asphalt when you peel the paper off, at least in the places I have seen it cored.

The Green River Shale I have seen ranges from blue gray to a light grayish brown, and up near Rio Blanco, has scads of insect fossils in it. (mostly gnats, bot fly larvae, and the occasional mosquito). There are supposed to be better bugs up near Douglas Pass, but the ones I found up there were weathered somewhat and not as nice as the small ones near Rio Blanco.

The deposit is considered to be lake bed sediments, and feathers and small plant fronds and leaves can be found in the Rio Blanco area as well.

For more information, this article is a start.

By contrast, the Bakken Shales (upper and lower) were laid down in a marine basin, and do not outcrop anywhere. They are completely contained in the subsurface. Considering the area of the Williston Basin, it is a huge area where oxygenation stopped and the organics were preserved to generate oil. Pressure and temperature, both a function of depth of burial, provided the mechanisms of oil and gas generation, with true vertical depths between roughly 8000 ft. and 10500 ft. being ideal in North Dakota. In the Elm Coulee Field in Montana the depths are a bit shallower, but the oil is there (there is only one Bakken Shale in most of the Elm Coulee field, the other having pinched out before you get that far west. The shale looks much the same as that in the deeper part of the Basin in North Dakota, black, vitreous to waxy, and breaks readily into small chunks, which can cause problems in a horizontal well because the hole will slough if you stray from the middle Bakken into either shale (upper or lower) and the drill string can get stuck--an expensive problem, necessitating drilling a sidetrack, and possibly causing the loss of a million or more dollars worth of downhole tools.

For more info on the Bakken, check out this website and wikipedia, which have pretty good basics.