In other words, the individual stripes were each deposited separately as horizontally layered sheets atop the ice while this berg was still attached to the much larger land mass from which it broke off and drifted out to sea. Each layer would then represent a different period of time. In this regard, it's very similar to layered sedimentary rock formations we see along highway road cuts, only they have broken off from their original source and floated out to sea. There are, however, isolated boulders known as 'glacial erratics' that have been transported vast distances by advancing ice sheets (over land). In fact, there are quite a few of these objects in the heart of Manhattan--in New York's Central Park. Some of the familiar boulders, however, are just large chunks left over from blasting done when they excavated underpasses to make roadways. Glacial erratics are often more rounded due to the abrasion that occurred during their long transport inside or at the base of the advancing ice. The blasted boulders are typically more jagged.
Finally, some of the true glacial erratics in Central Park originated from the Palisades of neighboring New Jersey. The rocks of the Palisades were once molten lava injected deep underground between pre-existing sedimentary rock layers. This happened as a great super-continent (Pangaea) was just beginning to split apart to form the Atlantic Ocean (~200 million yrs ago). Dinosaurs still existed at this time. OK, I know! Enough already. (don't ever get me started talking about rocks and earth history!)