172 GEOLOGY. 
sharks; one to that of skates, and another is remotely allied to the family of mackerels.’’ 
** No fossil sharks’ teeth having been found west of the Rocky mountains before, this discovery 
of a variety of species belonging to several genera of the family of sharks constitutes one of the 
most interesting additions to our knowledge that could have been obtained from that quarter; 
and the importance of these fossils to science is further enhanced by the peculiar relations they 
bear to similar fossils in the Atlantic States and in Europe, and to the sharks now living along 
the shores of the Old and of the New World.’ 
These fossils all differ from known species, and are described by Professor Agassiz under the 
following names: Echinorhinus Blakei, Scymnus occidentalis, Galeocerdo productus, Prionodon 
antiquus, Hemipristis heteropleurus, Carcharodon rectus, Oxyrhina plana, O. tumula, and Lamna 
clavata. It appears that a species of the genus Echinorhinus is now found in a fossil state for 
the first time ; the only hitherto known representative—the Squalus spinosus, of Linneus— 
being found only in the Mediterranean and the Atlantic, on the European and African coasts. 
Professor Agassiz observes, that ‘‘the discovery of a fossil species of this genus in the Tertiaries 
of the western slope of the Sierra Nevada is not only important as carrying back this curious 
type of sharks to a period older than ours, but also in disclosing the existence upon the Ameri- 
can continent of types in a fossil state known in the Old World only among the living. The 
fossil species of Echinorhinus differs from the living, having the main point of the tooth more 
prominent, and at the same time shorter, an appearance which arises from the less prominence 
of the marginal denticles.”” 
It is also an interesting fact that while no representative of the genus Scymnus has yet been 
found in the Pacific ocean, its former existence there is shown by the specimens. Professor 
Agassiz also identifies one of the specimens as a fragment of a tooth of the genus Zygobates, of 
the family of skates, with pavement-like teeth. No species of this genus, or the allied genera, 
have yet been observed in the Pacific ocean. Several fragments of bone which I picked up with 
these teeth are identified as belonging to the family of Scomberoides, remotely allied to the 
mackerels, but they are too imperfect to be more nearly identified. Other fragments obtained at 
the same time are bones of mammalia, but, with one exception, they were too small and un- 
characteristic to be identified with any degree of certainty. One of them is considered by Dr. 
Joseph Leidy, of Philadelphia, to be a portion of the crown of the molar tooth of a mastodon. 
Several small specimens of silicified wood were also found. - 
Age of the formation. —Mr. Conrad, after a careful examination and comparison of the fossil 
shells, considers that the formation should be referred to the middle Tertiary or Miocene He 
remarks that he does not find any recent species among them, nor any contained in an Eocene 
mn Professor Agassiz arrives at a similar conclusion from the examination of the sharks’ 
th, i R 
The original conditions of the deposition of these strata, so far as they are indicated by the 
fossils and lithological characters, are worthy of attention. The earthy materials surrounding 
the casts of the shells were not very fine, but consisted principally of coarse sand, mingled with 
pebbles, the perfection of the casts being secured by the infiltrated oxide of iron and a small 
portion of clay. The sand and clay had completely filled the interior of the most complicated 
shells, being found to have penetrated to the full length of the spires of long Turritelle. The 
shells were mingled together very closely, and in confusion. Oblique or diagonal stratification 
was shown in the stratum as well as in those above, thus proving the existence of currents 
changing in direction. The shells had evidently been drifted to that point and accumulated by 
