The West Coast was the leading edge of North America, and that is where mountains formed. Glaciation occurred in Africa during the Cretaceous. Streams became rejuventated in North America, and deltas formed on the coast. During much of the Tertiary, marine waters covered large parts of the southeastern United States. By late in the Cenozoic, North America had migrated far enough to the north for seasonal effects on the weather to become pronounced in the northern part of the continent.
Glaciers are gravity-driven.
The mineral, ice, accumulates and flows. Pressure can melt the bottoms of glaciers and enable them to glide. Louis Agassiz grew up in Switzerland observing mountain glaciers, also known as valley glaciers. In addition to these types, continental glaciers also exist, and this is is what created what is now Long Island's surface during the Pleistocene. Agassiz noticed rocks at the edge of the glacier as well as other rocks way down the valley past the glacier.