ForaiiilniU'ral Orif/in, Etc. — Hill. 17o 
(Trinity) sands showed brccciale or layers in laminate struc- 
ture, indicative of littoral origin or were accompanied by littoral 
faunas. All the other lower Cretaceous limestones are of a 
massive or pasty texture, unlaminated, and of varying liard- 
ness and purity, aiid wlien microscopically examined show an 
abundance of foraminiferal remains imbedded in a calcareous 
(calcite) matrix. 
The foraminiferio always exceeded in number the few 
molluscan remains, which were seldom found, thus clearly 
showing that these rocks are of chalky origin. 
The rocks of one horizon consist entirely of individuals of 
the species Tinoporus texana of Rammer, many of which are 
^'isible to the naked eye. For this horizon I propose the 
name of Tinoporus chalk. 
The excessive metamorphism which these chalks have 
undergone is due to several causes. In the vicinity of Austin 
and thence southwest to the Rio Grande, it can be attributed 
to excessive plication and igneous contacts. This is well 
shown even where the igneous rocks do not appear at the sur- 
face. In some places, however, as at Pilot Knob, southeast of 
Austin, the chalk of the upper Cretaceous is converted into a 
crystalline marble along the igneous contacts. In addition to 
the two great chalk deposits of the upper and lower Creta- 
ceous respectively, there are but three limestone horizons in 
the entire sedimentation of the two Cretaceous formations of 
the southwest of other than foraminiferal origin, and they 
compose but a small fraction of the entire thickness. The 
lowest of these, as above mentioned, is formed in the basal 
Trinity beds, and consists of fissile-laminated Hags, often com- 
posed of shell-breccia, seldom exceeding one foot in thickness. 
Analogous laminated limestone layers occur at the base 
of the upper Cretaceous in the fish bed (Benton) clays. These 
are the only two laminated (shallow water) limestone horizons 
in the immense develoi)ment of the two Cretaceous forma- 
tions. 
The third kind of non-foraminiferal limestones are segre- 
gations of calcareous matter, in layers or nodules, mostly 
in the uppermost arenaceous or glauconitic beds of the upper 
Cretaceous, as at Ripley, Mississippi, in Coddo creek, near 
Hearne, Arkansas, or in the Ponderosa marls of the Corsicanna, 
or Navarro bed, of Texas. These are formed by the lixiviation 
