Being In the middle image at the bottom

In the southwestern part of the map, along the Shenandoah River, the sediments are only Quaternary in age, yet they are surrounded by much older Cambrian sediments. How do you explain this?In the southeastern corner of the map, locate Rockville and Gaithersburg. Notice that they are separated by the Plummers Island Fault. Is Rockville moving atop Gaithersburg or is Gaithersburg moving atop Rockville?Find Martinsburg, WV, in the extreme northwest corner. Now locate Martinsburg, MD, which is just to the to the east of Harrison Island and Mason Island along a bend in the Potomac in the south central area of the map. Which is surrounded by the older rock?Locate Long Marsh Run just south of the West Virginia/ Virginia border on the southwestern side of the map. Which way is it flowing?How many different ages of rock would you encounter along its course?In the middle image at the bottom, to the far right, you see that the younger Prettyboy Schist lies beneath the older Mather Gorge Formation. How can older rock be found atop younger rock?Locate the oval, brown rocks near the center of the map. What geologic feature is this?