The gesture that performs vertical scrolling is called single-finger panning. When having no gesture support, the events will be "translated" to scroll wheel events. You will only see vertical events because there is no horizontal scroll wheel and horizontal panning is interpreted as dragging. See Windows Touch Gestures Overview (Windows)
] for an overview of gestures and the corresponding mouse actions.
messages are send for vertical events to implement enhanced panning as described at Improving the Single-Finger Panning Experience (Windows)