Bibliographical Notice. 37$ 



place as the lowest Cretaceous rock. Considerable care appears to 

 have been taken by Dr. Hayden in these observations, as it has been 

 supposed by Marcou that, in this zone of red leaf-bearing sandstone, 

 beds of Miocene and Jurassic age may have been confounded toge- 

 ther. In New Mexico, the equivalent of this group No. 1 has been 

 seen by Dr. Newberry to be overlain by Inoceramus-limestone con- 

 taining fossils thought by Marcou to be Jurassic ! Cretaceous group 

 No. 2 consists of dark grey fossiliferous clays, in Nebraska, with a 

 thickness of 200 feet, and contains Ammonites Alpinianus, A. per- 

 carinatus, Serpulal tenuicarinata, Inoceramus problematicus, Ostrea, 

 Fish-remains, &c. (pp. 69 & 72). (In the table of fossils at p. 81, 

 Ammonites Vermilionensis only is quoted for this group.) Along 

 the Big Horn, Laramie, and Wind River Mountains, from 800 to 

 1000 feet of black plastic clay, with beds of calcareous sandstone, 

 represent perhaps both No. 2 and No. 1 (p. 124). Group No. 3 in 

 Nebraska consists of Inoceramus-limestone (30 feet) passing upwards 

 into marl with Ostrea congest a (100 feet) ; fish-remains are abundant 

 throughout. In the west this group appears to be lost. Group 

 No. 4 is represented in Nebraska by dark fossiliferous clays, 350 feet 

 thick ; the lowest beds are locally lignitiferous ; and the lignites have 

 in some places been burnt, and the strata thereby altered (pp. 75 & 

 76, note). This group is widely extended, gives a sterile character to 

 the land, contains sandy seams impregnated with sulphate of soda, 

 and is rich in numerous well-preserved organic remains : of these 

 the chief are Mosasaurus, Nautilus Dekayi, Ammonites placenta, 

 A. Halli, Baculites ovatus, B. compressus, and very many other 

 Mollusks, &c. (See table of fossils, pp. 81 &c.) : the only yet known 

 Echinoderm of the Cretaceous rocks of the north-west occurs in these 

 beds, on the Yellowstone River. Group No. 5 succeeds No. 4 with 

 but little alteration in its fossil fauna; it is about 150 feet thick, 

 consists of very fossiliferous clay and sandy beds, with much irony 

 matter and numerous concretions : Belemnitella bulbosa, Nautilus 

 Dekayi, Ammonites placenta, A. lobatus, Scaphites Conradi, Bacu- 

 lites ovatus, Ostrea sub trig onalis, and many other Mollusks, &c. 

 (pp. 69, 79, 81 &c). 



On the western slope of the Rocky Mountains the series is repre- 

 sented by 600 to 800 feet of black clays, sandy marls, sandstones, 

 and limestones, alternating, and containing some lignitic seams. In 

 the middle and towards the top of the series are some Inoceramus- 

 limestones. The group has a general dip of about 20°, and passes 

 upwards imperceptibly into the great Lignitic Tertiary group. 



Some of the Cretaceous beds suffered erosion before the others 

 succeeded them ; and in some cases it is evident that the groups 

 Nos. 5, 4, & 3 were denuded before the deposition of the Tertiary 

 beds (p. 125) ; but, on the other hand, the beds of group No. 5, after 

 having gradually changed from a mainly argillaceous to an arenaceous 

 condition (from deep to shallow-water formations), pass, in some 

 instances without any apparent break, into the superincumbent 

 " Estuarine Tertiaries " : indeed, were it not that Baculites, Ammo- 

 nites, Inoceramus, &c, which abound in group No. 5, " are every. 



