298 



PROCEEDinOS OF THE 'NATtOVAL MUSEUM. vol. xxxvi. 



of the Jurassic, but Marsh's statement that " they occur in successive 

 deposits of the same general horizon, the smallest species below, the 

 largest above," " can not be verified, and is not borne out by the 

 structural characteristics of the typical specimens. Moreover, as 

 shown by the original field labels still remaining with the type 

 material, C. dispar, 0. 7nedius, and C nanus came from the same 

 quarry (No. 13) and in all probability were found at the same level. 

 Although the holotype of (\ ampins Avas found in the same general 

 area, it is from another quarry in a region where it is difficult to 

 trace stratigraphic horizons. It also appears from Marsh's own 

 writings that he was not quite clear as to their stratigraphic posi- 

 tions, for in 1879 ^ at the close of his description of C amplus, he 

 says: " The remains of the present species are from a lower horizon 

 in the Jurassic than those described above \C. dispar], but within 

 the limits of the Atlantosaurus beds." He thus places the larger 

 species at a lower level, which is contradictory to his later statements. 



Fig. 48. — Section of Qi'.\I!T!y 1."^. M.vde p.y Mk. Fred Browx ix 1SS4. 



Since Quarry No. 13 has furnished four of the holotypes per- 

 taining to the genus Oamptosaurus, besides a vast quantity of other 

 material, the exact stratigraphic position of the bone-bearing layer 

 is of considerable interest. A clue to the position of this layer was 

 found in a rough section of the strata exposed in working this quarry, 

 made by Mr. Fred Brown in 1884 (see fig. 48). 



The fossils occur here in a layer of sandy cla}^," as I have deter- 

 mined from the matrix, still adhering to bones, and, as seen in 

 Brown's section, the bone-bearing layer (" pay streak ") is inter- 

 calated between layers of marl or clay, green below and brownish 

 above, all three layers lying between bands of sandstone. 



« Amer. Journ. Sci., XLVIII, 1894, p. 85. 

 6 Idem, XVIII, 1879, p. 503. 



^ On pTige 199 of the present paper, Mr. W. II. Keed is quoted as also noting 

 the sandy nature of the matrix in which the fossils occur as being unusual. 



