The Metacomet Ridge was the product of several massive lava flows hundreds of feet deep that welled up in faults created by the rifting apart of North America from Eurasia and Africa. The basalt floods of lava occurred over a period of 20 million years. Erosion occurring between the eruptions deposited deep layers of sediment between the lava flows, which eventually lithified into sedimentary rock. resulting "layer cake" of basalt and sedimentary sheets eventually faulted and tilted upward. Subsequent erosion wore away the weaker sedimentary layers a faster rate than the basalt layers, leaving the abruptly tilted edges of the basalt sheets exposed, creating the distinct linear ridge and dramatic cliff faces visible today. The best way to imagine this is to picture a layer cake tilted slightly up with some of the frosting (the sedimentary layer) removed in between. The sedimentary rock of the Metacomet ridge is well known for its fossils, especially dinosaur tracks.