CLASSIFICATIO^' OF THE JURA. 411 



Jura the following series : Lias or Lower Jura, Oolite or Middle Jura 

 and Malm or Upper Jura. 



In the Lias we have the Lower Lias and L^pper Lias, but the Middle 

 Lias has not 3^et been discovered. 



In the Oolite the Ta3dorville fauna may possibly represent what Stein- 

 mann calls the Lower and Middle Oolite, which is about equivalent to the 

 Inferior Oolite of England. The Upper Oolite, if it exists in America, 

 has not yet been distinguished. 



In the Malm we can distinguish at Taylorville the Callovian or Kello- 

 way, the lowest series of the Upper Jura, and what seems to be the equiva- 

 lent of the Corallian, a late stage of the Oxfordian series in Europe. 



The basin of the Black hills contains the Lower Oxfordian, and in 

 Alaska the same occurs with probably other members of the Jura, not 

 yet distinguished. Their age appears to be in large part younger than 

 the Callovian of Taylorville and older or only in j)art contemporaneous 

 with the supposed Corallian of that locality, as previously stated by me.^ 



The Gold Belt series of slates is apparently in large part, if not as a 

 whole, later in age than the rocks just referred to. It includes part of 

 what the Russians regard as the youngest Oxfordian, and also the Port- 

 landian or Kimmeridgian and possibly even including in part or as a 

 whole the equivalent of their Volgian, the youngest stage of the Tithonian, 

 the topmost series of the Jura in Europe. 



In other words, it may be said that the Malm or upper Jura apj^ears 

 in this country to have at least four very distinct faunas, that of the 

 Bicknell sandstone at Taylorville, that of the Black hills and Alaska, 

 that of the Hinchman tuff at Taylorville, and that of the Mariposa and 

 Colfax regions in California. The latter can be subdivided, as has been 

 done above, according to the Russian classification, into several minor 

 faunas, but as a whole they are obviously younger than the fauna of the 

 Bicknell sandstone which I have compared with the Kelloway or 

 Callovian. 



It is not practicable to tabulate these views without giving to them an 

 appearance of greater precision than they deserve, but nevertheless I 

 have attempted to do this in order to put them more clearly before the 

 minds of paleontologists. 



I desire again, in this connection, to say that the subdivision of the 

 Gold belt slates rests on very slender information and is merely sugges- 

 tive. I am especially doubtful with regard to the relative age of the 

 Colfax slates, and whether they are really the youngest or the oldest of 

 the Gold Belt series may be considered as unsettled. In fact, I put them 

 in the table in their present definite shape more to excite the attention 

 and interest of collectors in this field than for any other purpose. 



* Jura and Trias at Taylorville, p. 410. 

 LVIII— Bull. Geol. Soc. Am., Vol. 5, 1893. 



