156 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Gryphaea Tucumcarii is Jurassic. Moreover, it is the uppermost 
subdivision of the American Jura. The strata below, and between 
it and the Trias, belong to the Jura also, and are synchronous with 
the Bosque division and very likely with the Fredericksburg division 
of Texas. 
The Jurassic series of Texas is the same as the one I observed in 
185*8 at the Tucumcari area, at Canon Blanco, and near Covero, 
New Mexico. It follows alono- the banks of the Rio Pecos down to 
o 
western Texas, where it occupies large surfaces from Kent and Leon 
Spring, then turns towards the northeast by Austin, Bosque County 
and Glen Rose, reaching as far as Pike County in Arkansas. It forms 
a large band often covered by Cretaceous beds, but outcropping now 
and then by denudation and erosion of the overlying Cretaceous 
strata. 
I wish to add a word in regard to the Lower Cretaceous of Texas, 
which I was the first to recognize and refer to its proper position in 
the stratigraphic tables of American historic geology, as long ago as 
1853. It is certain that the details of its stratigraphy require a care¬ 
ful revision and a complete recasting, and that the time for calling 
every Gryphaea found in Texas, Gryphaea Pitcheri has passed. 
That unfortunate name has been applied to at least six or seven 
entirely distinct species, three of them Jurassic and three or four 
Cretaceous. 
One example more of paleontological confusion. The Gryphaea 
sinuata var. americana of the Washita limestone (Marcou, Geology 
of North America, p. 87—38, pi. 3, fig. 1, 1858) is not the same as 
the JExogyra americana var. quitmanensis Cragin (Invert, paleon¬ 
tology of the Texas Cretaceous, Fourth annual report, 1893, p. 183, 
pi. 31). We have here two distinct species, just as in England and 
France we have the true Gryphaea sinuata of the Lower Greensand 
and another similar species found in the Jurassic upper Kimmerid- 
gian of Boulogne-sur-Mer and Speeton (Yorkshire). 
The constant mention bv Mr. Ilill and bv the members of the 
Geological survey of Texas of fossils passing from one great division 
to another, and roaming, several of them, through what they call 
the whole Lower Cretaceous, that is to say, through more than two 
thousand feet of strata, implies a material impossibility, which should 
receive careful attention in determining fossils. ' Erroneous paleon¬ 
tology together with erroneous stratigraphy and erroneous lithology 
has long enough prevented progress in Texas geology. 
