. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. THE UPPER SILURIAN PERIOD. 117 Generalised Section of the Upper Silurian Strata OF Wales and Shropshire. Fig. 57-. J Base of Old Red Sand- I stone. — Tile-stones. — Uppei- Ludlow Rock. Aymestry Limestone. — Lower Ludlow Rock. — Wenlock Limestone. Wenlock Shale (Denbigh- shire Flags and Grits of North Wales). Woolhope Limestone. Tarannon Shales. May Hill Sandstone. Llandovery Rocks. (3) Niagai-a Group.—This group consists typically of a series of argilla
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. THE UPPER SILURIAN PERIOD. 117 Generalised Section of the Upper Silurian Strata OF Wales and Shropshire. Fig. 57-. J Base of Old Red Sand- I stone. — Tile-stones. — Uppei- Ludlow Rock. Aymestry Limestone. — Lower Ludlow Rock. — Wenlock Limestone. Wenlock Shale (Denbigh- shire Flags and Grits of North Wales). Woolhope Limestone. Tarannon Shales. May Hill Sandstone. Llandovery Rocks. (3) Niagai-a Group.—This group consists typically of a series of argillaceous beds ("Niagara Shale") capped by limestones ("Niagara Limestone"); and the name of the group is derived from the fact that it is over Hmestones of this age that the Niagara river is precipitated to form the great Falls. In places the Niagara group is wholly calcareous, and it is continued upwards into a series of marls and sand- stones, with beds of salt and masses of gypsum (the " Salina Group "), or into a series of magnesian limestones ('' Guelph Limestones"). The Niagara group, as a whole, corresponds unequivocally with the Wenlock group of Britain. (4) Lower Helderberg Group.—The Upper Silurian period in North America was terminated by the deposition of a series of calcareous beds, which derive the name of " Lower Helder- berg" from the Helderberg mountains, south of Albany, and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicholson, Henry Alleyne, 1844-1899. Edinburgh, London, Blackwood
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