MINGLING OF TYPES IN THE HAtlDGRAVK. 40 



O 



of the sutures of the carapace, but the surface has the rare sculpturing 

 of punctation in place of the usual tuberculation found in most species 

 of this genus, a peculiarity also characteristic of G. punctata. Such forms 

 as these and the evidently close alliance and probable continuity of the 

 fauna through migration with that of the Mormon sandstone suggest 

 that the Hardgrave sandstone should he classed as upper Lias in spite 

 of the large number of forms which are represented by species occurring 

 also in the lower and middle Lias in Europe. 



The homogeneous character of the rock and the association of fossils 

 found in the larger masses of it led also to the conclusion that it repre- 

 sented only one bed in the upper Lias, but such minute researches as 

 would have established this beyond question were not practicable. 



Middle Jura or Oolite: Thompson Limestone {Opis Led). — Mr. Diller's 

 dose and repeated investigations of the stratigraphy have placed the 

 Opis bed below the Mormon sandstone in the chronologic series, and 

 my studies, although they led me to incline to the opinion that the 

 fauna was younger, have not succeeded in bringing to light any evidence 

 that can be said to contradict bis conclusions. The presence of a large 

 form of Nerinea with the columella, showing the typical ridges of the 

 normal forms of this group, indicate that this limestone is not older than 

 the inferior Oolite, and if. as seems to be the case, it is older than the 

 Mormon sandstone it will probably be proved to be a member of the 

 inferior Oolite. 



A large species of Oyy/.s is as abundant in some places as the Nerinea, 

 and this genus, winch is recorded in Europe as beginning in the Trias, is 

 usually small throughout the lower and middle -Jura. The only Euro- 

 pean species approximating to that of this limestone is the Opis paradoxa, 

 as figured by Buvignier* which occurs in the Corallian of the upper 

 Jura. A species of Terebratula, apparently identical with the large char- 

 acteristic species of the Mormon sandstone, also occurs abundantly in 

 this bed. There are also a number of small gasteropoda and other fos- 

 sils requiring further investigation. 



Mor n Sandstone ( Sphssroceras Bed ). — This bed contains the remains 



of a more varied fauna than that of the Hardgrave sandstone, in some 

 places, especially upon spur 8 of Mr. Diller's map, the fossils arc in ex- 

 cellent preservation; but in some localities merely superficial work does 

 not give good results, the rock being apt to be very friable. Here as 

 elsewhere tic greatesl treasures await resurrection at the hands of those 

 able to dig deeply into the stony matrix. 



It is more difficull to poinl out the characteristic lossils in this bed 



Stat. geol., mill., metal, el pal. 'In Depart, tie la Meuse, 1852, pi. 13, figs. 37-42. 

 I.\ Bi li.. i Soi . Vm., Vol. 3, 1891. 



