ABSTEACTS OF PAPERS 105 



Discussed by D. F. Higgins, who drew attention to the fact that lathe 

 and planing-machine mechanics use water on the cutting edge to produce 

 a polish on steel. Dry cutting gives a dull surface, often pitted. 



RED LIMESTONES AND THEIR GEOLOGIC SIGNIFICANCE 

 BY J. J. GALLOWAY 



{Abstract) 



Red limestones occur in nearly every system from Cambrian to Quaternary, 

 but their areal extent is usually small, and they constitute but a small per- 

 centage of the limestones of the geologic column. In the few cases which have 

 been noted by geologists, the origin of red limestones and their geologic sig- 

 nificance have not been discussed ; or the unusual color is attributed to organic 

 acids brought to the sea from the land during the deposition of the limestone, 

 or to atmospheric oxidation due to oscillations of the sealevel during their 

 deposition. 



Many shades of red are represented : pink, scarlet, orange, brown, salmon, 

 purple, maroon, and rose. Examples are: the Smith Point limestone (Lower 

 Cambrian) of Newfoundland, bed Id of the Weeks formation (Upper Cam- 

 brian) of Utah, the Manitou (Beekmantown) limestone of Colorado, the 

 Holston marble (Middle Ordovician) of Tennessee, the Moccasin limestone 

 (Black River) of Virginia, the Orthoceras limestone (Ordovician) of Sweden 

 in part, the Brassfield limestone (basal Silurian) of Kentucky, the Chimney 

 Hill limestone (Brassfield) of Oklahoma in part, the Perce beds of the Grand 

 Greve limestones (early Oriskanian) of Gaspe, the Minnekahta limestone 

 (Permian) of the Black Hills, the Chase limestone (Permian) of Oklahoma, 

 the Dolores limestone (Permian) of Wyoming, the Halstatt limestone (Trias- 

 sic) and Hierlatz limestone (Jurassic) of Austria, the Red Chalk (top of 

 Lower Cretaceous) of England, the salmon-colored limestone (Miocene) of 

 the Sierritas of Yucatan, the sepia-colored limestone (Pliocene and Quater- 

 nary) of northern Yucatan, and many brecciated marbles in America and 

 Europe. 



The color is due to limonite and hematite. Lithologically, red limestones 

 vary from porous and chalky to dense and brittle, but are commonly earthy 

 or nedular, massive and not well bedded, frequently brecciated by crushing, 

 and are recemented. They are all fine grained except the crinoidal varieties. 

 They are as fossiliferous as other kinds of limestone, and the fossils are par- 

 tially replaced by lime or iron oxide and are frequently fragmental, worn, or 

 crushed. Chemically, the limestones vary from nearly pure calcium carbonate, 

 as the pink chalk of Yucatan, to very impure, with as much as 40 per cent of 

 iron oxide, as the Red Chalk of England, and with much silica and clay, as 

 the Manitou limestone. Organic matter other than calcium carbonate is absent. 



Red limestones do not occur in beds of great horizontal extent, like ordinary 

 limestones, but the outcrops only are red; they are not encountered in wells 

 or tunnels except where a crushed zone is penetrated. They have long been 

 exposed to weathering (most of the examples mentioned) or occupy uncon- 

 formities where they have been subjected to weathering (Red Chalk and 



