398 A. HYATT— TEIAS AND JURA IN THE WESTERN STATES. • 



fore that the Aptychi found in the Ammonites bed of Sailors canyon 

 prove the age to be Liaspic is not conclusive. These earlier opercula 

 were all found to be carbonaceous, and consequently it is inferred that 

 they must have had a horny or tough cuticular basis. 



A peculiar leathery or horny and univalvular operculum called the 

 AnaptTjchus was introduced in the Arietidse of the lower Lias and con- 

 tinued in the middle Lias, and it has been reasonably supposed that 

 these were the forerunners of the calcareous bi valvular opercula of the 

 shells of the succeeding stages. 



The bivalvular rugose Aptychi at Sailors canyon are represented solely 

 by impressions, and consequently their exact constitution cannot be 

 proved. Whether they were really calcareous like the similar rugose 

 forms of the Lias and later Jura or whether they were of a horny tex- 

 ture must remain undecided, and this is a possible stumbling-block in 

 the way of any opinion based solely upon them. 



It must also be noted that if this fauna be Triassic, it is remarkable 

 for not containing any of the characteristic cephalopods of that system, 

 and none exactly comparable with those of any other Triassic fauna, 

 either in this country or in Europe. 



The specimens of Ammonitinse found by Dr Curtice below the tuffs 

 that form the summit of Snow mountain, the highest fossil locality in 

 American canyon, are similar in part to those of Sailors canyon, and 

 indicate a somewhat distinct yet connected and probably j^ounger Am- 

 monitoid fauna. 



Gryphsea Bed. — The specimens described as Gryphsea, and found in 

 rocks supposed by Dr Curtice to be younger than the Ammonites beds of 

 Sailors canyon but older than those of Snow mountain, give evidence for 

 the Liassic age of these rocks, true Gryphxa not having been hitherto 

 found below the lower Lias. 



AGE AND FAUNAL RELATIONSHIPS OF THE TWO AREAS. 



Although it ig safe to decide positively with regard to the relative age 

 of the different strata of the Sailors canyon series and that the Monotis 

 and Daonella beds contain forms usually regarded as Triassic, the facts 

 just recited are of such a nature that the age of the beds containing 

 Ammonitinse and Aptychi cannot be asserted except within certain 

 limits. Whether they .are exclusively upper Triassic or exclusively 

 Liassic, or a mixture of the fossils of both these faunas, must remain un- 

 determined until the sutures of these fossil shells can be discovered 

 It is, however, obvious that there are, so far as they have been explored, 

 no fossil beds in American or in Sailors canyon which are younger than 

 the upper Lias. 



