age of the hardgrave sandstone. 401 



The Jura. 



Lower Jura or Lias ( Hardgrave Sandstone). — The Hardgrave sandstone 

 contains the remains of a very abundant fauna and the fossils are suffi- 

 ciently well preserved. 



The most abundant species are the following: Pecten acutiplicaius, 

 Meek, is to he expected wherever this sandstone occurs and can lie called 

 its characteristic fossil in this region : Entolium meeki is perhaps the next 

 in abundance and is almost as widespread in distribution ; Pin mi expansa 

 is not found everywhere, hut it forms banks like Ostrsea or Unio in some 

 places and is often found associated with the two above named. 



The age of the Hardgrave has been determined by cumulative evi- 

 dence. That it was probably a member of the Lias, as previously stated 

 by Professor Jules Marcou, became evident after a preliminary examina- 

 tion of the fossils, but the facts leading to the conclusion that it is more 

 likely a member of the upper Lias than of the lowest Lias were more 

 difficult of acquisition. It contains many fossils having affinities with 

 those of the lowest or infra Lias, and the Modiola and Mytilus might even 

 have occurred in the uppermost Trias or Rha?tic. On the other hand, 

 some forms have very close relations to the same genera as they appear 

 in the Mormon sandstone, or Oolite, of the same locality. Pimm, Ger- 

 villia, Ctenostreon, Entolium, Trigonia and Cidaris show an assemblage of 

 upper Lias types. The species of Entolium and Ctenostreon are closely 

 related to those of the Oolite above, and one species of Trigonia resembles 

 the young of a species from the Oolite of western Europe. The most 

 conclusive evidence, however, is furnished by the single well preserved 

 specimen of Glyphea, which 1 was so fortunate as to find in the typical 

 locality close to the village of Taylorsville, and the Goniomya, allied to 

 G. v-scripta, Agassiz. 



The II' species exhibited, which were selected from the collections of 

 the Geological Survey, do not represent the entire fauna. I have still 

 farther restricted the list given below to those species which are either 

 characteristic or have been described and figured or can he closely com- 

 pared with representative European species: 



Taylorville, California. Europe. 



Mpntlivaultia, n. sp. .(?). M. haimei, chap, el Dewal.j lower 



Lias. 

 Ostrsea, sp. Ostrsea irregularis, Chap, el Dewal. ; 



inferior Lias to middle Lias. 

 Ostrsea, \\. sp. Ostrsea arietis, Quenst.; lower Lias. 



Anomia, n. sp. Anomia striattda, Terq. el Piette; 



lower Lias. 



