Here's the bottom side of the Laurentian fragile fern. The dots here are the spore producing sori. The identifying glands are too small to see. This is called Laurentian because it occurs along the Great Lakes/St. Lawrence River drainage. That system marks the southern reach of the Laurentian Shield, more often called the Canadian Shield. That is a huge area of the earth's shield that was exposed by the last glaciation. Significant parts of it are still exposed, or only covered with thin soil. The area stretches from that southern reach across much of northeastern Canada. The house-sized outcrop this fern was growing on was but a tiny bit of that shield.