224 Cincinnati Society of Natural History. 



cement. These beds undulate in low synclinals and anticlinals, having- 

 in general a northeast and southwest direction, and rise in some places 

 to an elevation of 400 feet above the sea. The^^ are probably about 

 500 feet in thickness. The lower half of this thickness, which con- 

 tains the limestone beds, and also certain hard beds of conglomerate 

 and concretionary calcareous sandstone, may be regarded as an equiv- 

 alent of the Bunter Sandstone ; while the upper portion, consisting 

 principally of soft red sandstone, with some beds of fine grained con- 

 glomerate may be regarded as corresponding to the Keuper. 



These beds rest conformably upon the newer coal measures without 

 the intervention of the Permian. They appear to have been deposited 

 in a shallow sea area, not improbably coincident with the Southern 

 Bay of the Gulf of St. Lawrence, limited to the north by the Magdalen 

 Islands and the banks in their vicinity, which represent an old Lower 

 Carboniferous outcrop. Their materials were derived from the waste 

 of red sandstones and marls of the Carboniferous, and have been thrown 

 down with sufficient rapidity to prevent the coating of red oxide of 

 iron from being removed by abrasion, or hy the chemical action of 

 organic matter. The dolomitic character of some of the coarse lime- 

 stones may either indicate the occurrence of occasional isolated 

 basins and depositions of magnesia from sea water, or may have been 

 connected with the outburst of igneous matter in magnesia, like the 

 dolerite of Hog Island, near to which place the beds richest in mag- 

 nesia were observed. 



In 1872, F. B. Meek* described from the Jurassic, at Lincoln Valley, 

 near Fort Hall, Idaho, Aviculopecten idahoensis. 



In 1873, Dr. F. V. Hayden estimated the thickness of the Jurassic, 

 on the Missouri, below the Canon at the Three Forks at 1,500 feet. A 

 section, in Spring Canon, on the headwaters of the Gallatin river in 

 Montana, of limestones, sandstones, quartzites and conglomerates, dis- 

 plays a thickness of 425 feet, followed below by 65 feet of Triassic age.f 

 And F, B. Meek described from Montana Gervillia montanensis, Go- 

 niomya montanensis, Myacites suhcompressus, Pholadomya kingi, 

 Trigonia americana, T. montanensis, and Volsella suhinibricata. 



In 1874, Dr. Hayden;]; estimated the thickness of the Triassic on 

 Eagle river, consisting of brick-red sandstones and clays at from 1,200 

 to 1,500 feet, and above them 200 feet or more of Jurassic rocks, suc- 



'•' 5th Rep. Hayden's U. S. Geo. Sur. Terr. 

 t 6th Rep. Hayden's U. S. Geo. Sur. Terr. 

 t 7th Rep U. S. Geo. Sur. Terr. 



