MIDDLE AND UPPER ORDOVICIAN. 201 



[Part of] synoptical table of geological formations about Montreal, Canada — Continued. 



System. 



Silurian. 



[Unconformity. 



Ordovician. 



[Unconformity." 

 [Pre-Cambrian.] 



Formation. 



Lower Helder- 

 berg. 



Lorraine. 



Utica. 



Trenton. 



Black River. 



Chazy. 



Calciferous. 



Potsdam . 



Character of strata, etc. 



Light-gray impure sub- 

 crystallineand altered 

 limestone, as small 

 outliers. 



Black or dark-brown and 

 buff-weathering shales 

 and arenaceous, beds 

 and mudstones; fossil- 

 iferous. 



Dark-brown and black 

 bituminous shales or 

 pyroschists with im- 

 pure limestone bands 

 at base; fossiliferous. 



Dark-gray impure fossil- 

 iferous limestones and 

 shales extensively 

 quarried for building 

 purposes; at times 

 semicrystalline. 



Light-gray weathering, 

 dark-gray and black 

 impure fossiliferous 

 limestones; building 

 stone. 



Light and dark gray 

 semicrystalline im- 

 pm-e fossiliferous lime- 

 stone; useful for build - 

 .ing purposes. 



Dark-gray, buff and yel- 

 low weathering impure 

 earthy and semicrys- 

 talline limestones, for 

 the most part magne- 

 sian, and nolding nu- 

 merous crystals filling 

 cavities; lower meas- 

 ures arenaceous. 



Light-yellow and rusty- 

 weathering sandstones 

 and conglomerates oc- 

 casionally present at 

 the base and along cer- 

 tain divisional planes 

 of stratification. 



Characteristic fossils. 



Lepta^na rhomboidalis, Stro- 

 phodonta varistriata, Stro- 

 'phonella punctulifera, Pen- 

 tamerus (Sieberella) galeatus, 

 Atrypa reticularis, Platyo- 

 stoma depressum. 



Favistella stellata, Orthograp- 

 tus quadrimucronatus, Zy- 

 gosjpira headi, Pterinea de- 

 missa, Byssonychia radiata, 

 Clidophonts planulatus, 

 Orthodesma parallelum, 

 Protowarthia cancellata, 

 Cyrtolites orruitus. 



Leptograptus Jlaccidus, Lep- 

 tobolus insignis, Schizo- 

 crania filosa, Comulites im- 

 maturum, Endoceras proteri- 

 forme v. tenuistriatum, Tri- 

 arthrus becki, Trocholites 

 ammonius. 



Glyptocystites logani, Hetero- 

 crinus tenuis, Pachydictya 

 acuta, Phylloporina trenton- 

 ensis, Prasopora selwyni, 

 Plectambonites sericea, Tre- 

 matis montrealensis, Dal- 

 manella testudinaria, Lin- 

 gula nciniformis, Parastro- 

 phia hermplicata,' Rafines- 

 quina altemata, Platystro- 

 phia lynx, Cyclonema mon- 

 trealense, Trochonema um- 

 bilicatuvi, Conularia tren- 

 tonensis, Trinucleus con- 

 centricus, Isotelus gigas, 

 Calymene senaria. 



Tetradium fibratum, Colum- 

 naria halli, Stromatocerium 

 rugosum, Helicotoma plan- 

 ulata, Cyrtodonta huronen- 

 sis, Bathyurus extans. 



Bolboporites americanus, Ma- 

 locystites murchisoni, Blas- 

 toidocrinus carcharisedens, 

 Camarotoechia plena, Heber- 

 tella borealis, Dinorthis 

 platys, Bathyurus angelini. 



Orthisina grandmva Billings, 

 Pleurotomaria calcifera B., 

 P. canadensis B., Hormo- 

 toma anna B., Metoptoma 

 simplex B., Orthoceras la- 

 mar cki B., Amphion salteri 

 B., Bathyurus cybeleB., Ri- 

 beiria calcifera B., Leper- 

 ditia anna B . 

 Scolithus canadensis BUI., Pro- 

 tichni t e s multinotatus 

 Owen, P. Uneatus Owen, 

 P. octonotatus Owen, P. 

 septem-notatus Owen. 



Thickness. 



Only a few feet thick, 

 preserved near some 

 protecting dike of erup- 

 tives. 



From a few feet to 400 or 

 600 feet, and runs to 

 the south and west. 



Between 100 and 450 

 feet. 



Between 400 and 500 

 feet. 



About 75 feet. 



Between 150 and 200 

 feet. 



Between 200 and 250 

 feet. 



Between 200 and 300 

 feet. 



