Answer: Around 400 million years ago, the Avalon terrane smashed into the Nashoba terrane. This collision resulted in immense heating and squeezing of the rocks in the vicinity of this collision. The heat must have been high enough to partially melt the rock, so new crystals formed. The white veins running through the basalt are likely the result of this recyrstallization. The heat and pressure also made the white rock become more brittle.