Mary Bsetzula, age 10, of S. Williamsport, Pennsylvania, for her question:
What kind of rock formations are under Williamsport. Pennsylvania?
The scenic surface of Pennsylvania sits on a multitude of buried mineral treasures. Leafy forests crowd its countless slopes and fertile farmlands nestle in its gentle valleys. The city of Williamsport stands where the ancient Allegeny Plateau dips down to a crustal formation of swooping valleys and ridges.
The rocky formations to the earth's crust are pages of an immense planetary diary. Their crusty, crumpled pages tell the geological history of our planet dating back through billions of years. Layer by layer, they reveal immense upheavals through vast areas of the earth's crust. The rocky formations below Williamsport are folded into the crusty pages below all of Pennsylvania. And this part of the rocky diary is part and parcel of the ancient chapter that records the stupendous upheavals that formed the massive Appalachian Mountains.
The earliest pages of the diary, billions of years old, were crushed below layer upon layer of assorted rocks that formed in later chapters. Massive mountain¬making bent the crusty pages, cracked them and folded them like broken sandwiches. In parts of Pennsylvania, ancient layers from deep below were lifted in great slabs and shoved several miles westward over the surface. The growing mountains covered the map with a hodgepodge of cliffs and gorges. Volcanoes added layers of lava.
For part of its history, this region was a long, shallow ditch often swamped by draining rivers and invaded by the sea. These waters added deposits of limestone and sandstone that were later compressed into slates and shales. The growing moun¬tains bent these sedimentary rocks into crusty ups and downs. Meantime the weather wore down their loftiest peaks and washed more sedimentary soils into the valleys.
Some 250 million years ago, the slopes and swampy hollows of the young mountains were covered with ferny trees and giant horsetails. There were scorpions and insects; huge dragonflies zoomed through the air and whopping salamanders wallowed in the mud. These were the ancient coal making forests. As the restless young mountains grew, the layers of rock were shuffled again and again. Layers and layers of coal were sand¬wiched between rocky pages of volcanic and sedimentary rocks. Deposits of petroleum, iron ore and other valuable minerals also were folded in.
As far as one could tell from looking at it, the stupendous job was finished about 200 million years ago. The roughly parallel ranges of the Appalachians curved across Pennsylvania from the northeast to the southwest, forming a rugged tableland cut with deep gorges. Williamsport stands where the northern arm of the Susquehana River skirts the eastern edge of this tableland. The forested slopes to the north cover broken cracks in the old rocky sandwiches. To the south lie rolling farmlands with limestone deposited by ancient seas and rich silty soils washed down from the ridges.
On every side, Williamsport is enfolded within the ranges of the northern arm of the stupendous Appalachian chain. Steep slopes reveal jumbled slabs of assorted rocks. Granite outcroppings tell of the fiery old volcanoes. Coal beds tell of ancient forests. Sandwiched layers of limestone tell us of past invasions of the sea. Young geologists in Williamsport are surrounded by fabulous field trips. In one direction or another, they can find almost every type of crustal formation and an assortment of rocky minerals.