A second large package of rocks seen in the Geopark region formed in deeper water, on the continental slope that surrounded Laurentia, and beyond it on the gently sloping continental rise, in water depths from 200 m to perhaps 5000 m below sea level.
These rocks include much larger amounts of mud, tiny mineral particles originally eroded from Laurentia but wafted out to sea where they settled in the deep, quiet water. However, every so often the quiet of the continental slope was interrupted by an underwater avalanche of sand or gravel that came speeding down from the edge of the continental shelf. These tremendously powerful avalanches occur on modern continental margins from time to time and are known as turbidity currents (usually carrying sand or small lime particles) or debris flows (carrying larger pieces of rock). The deposits of these currents produce rocks with a characteristic layered or stripy appearance, which can be seen in many rock outcrops on the highways and coastal cliffs of the Bay of Islands. The rocks of the slope succession were intensely folded and faulted during the building of the Appalachian mountains, but the following succession has been pieced together by geologists, from top to bottom.
- Western Brook Pond Group: Early to Middle Ordovician sandstone and mudstone laid down as the Appalachian mountains were starting to form.
- Cow Head Group: Middle Cambrian to Early Ordovician layered limestone and mudstone laid down on the continental slope. Locally the mudstone is rich in fine grained quartz, forming a hard rock called chert, prized by early humans for tool making. The Cow Head group comprises the deep-water equivalents the Port au Port and St. George Groups on the shelf.
- Curling Group: early Cambrian sandstone and mudstone also laid down on the continental slope, equivalent in age to the Labrador Group on the shelf.
(Groups and formations are always named after places, but sometimes the same layer will be given two different names in two different places. Only later do geologists decide that the two names have been given to a single layer. For this reason, older publications refer to the Cow Head Group in the area of the Bay of Islands by the alternative name Northern Head Group.)
Cabox Geosites within the Slope Succession include:
