268 The American Naturalist. [March, 
flint, with fossils of Huronian and Devonian ages. The Middle Eocene 
(Nummulitic Limestone) beds appear to follow on those of Cretaceous 
age without a discordance, but there is a real hiatus notwithstanding 
the apparent conformity, as shown by the complete change of fauna. 
In Philistia a calcareous sandstone in which no fossils have been dis- 
covered is referred to the Upper Eocene; for the Miocene period was 
a continental one, when faulting and sliding were taking place, and the 
main physical features were developed—e. g., the formation of the 
Jordan-Arabah depression is referable to this period. i 
In Pliocene times a general depression of land took place to about 
200-300 feet below the present. sea-level, and littoral deposits were 
formed on the coasts and in the valleys. To this period belong the 
higher terraces of the Jordan-Arabah valley. The Pliocene deposits 
consist of shelly gravels. Later terraces were formed at the epoch of 
the glaciation of the Lebanon Mountains, when the rainfall was exces- 
sive in Palestine and Arabia. 
The volcanoes of the Jaulân, Hauran, and Arabian Desert are con- 
sidered to have been in active operation during the Miocene, Pliocene, 
and Plistocene periods, but the date of their final extinction has not 
been satisfactorily determined. (Geol. Mag., Jan., 1893). 
The Vertebrate Fauna of the Ordovician of Colorado.— 
Mr. Charles D. Walcott has recently published a paper on the verte- 
brate fauna in strata of Ordovician age near Canyon City, Colorado, 
already noticed in Tae Narurauist. The fossils consist of what 
appear to be the plates and scales of fishes and the ossified chordal 
sheath of a fish allied to the recent Chimera. The remains occur in 
a sandstone which is correlated with the lower Trenton and the lower 
Bala of Wales. Microscopic sections of a dermal plate belonging to 
an Asterolepis-like form, examined by Dr. Otto Jaekel, show (1) the 
dentine tubules that are characteristic of vertebrates ; (2) the occurrence 
of true osteoblasts, which exclude the forms from the Elasmobranchii, 
and relegates them to other low divisions of the fishes ; (3) the absence 
of enamel and the distinct concentric lamination of the dentine tubules 
which indicate a low stage of development. 
In view of the objections that can be made to -a classification based 
entirely upon the characters of the dermal plates and scales Mr. Wal- 
cott has made his classification tentative and has only outlined the 
characters of the fragmentary remains. For the present, then, the 
fossils will be known respectively as Dictyorhabdus priseus, a supposed 
chimaeroid, and Astraspis desideratum and Eriptyehus americanus, 
