Thanks to Texas Geology for the information below.
"The Texas of today is the result of about six hundred million years of geologic history. Paleontologists are scientists able to reconstruct earth history by examining fossils found in layers of rocks from different periods of geologic history. It has been estimated there about about half a million different types of fossil remains in Texas.
A look at the fossil record of Texas shows clearly, the Texas of the past differs radically from the Texas of the present. Where people live and work, corals, trilobites, and numerous other fossils once lived in huge seas. Where there are only gently rolling hills, large mountains once stood.
In order to understand the ancestry of Texas fossils, it is necessary to study the geography and origin of the region which they were found. The geologic history of Texas, like the rest of the earth, is recorded primarily in marine sedimentary rocks. These rocks were formed from sediments of shallow seas which covered parts of the state at various times in the earth's history. By studying these rocks, geologists have established a geologic column for Texas. A geololgic column refers to the total succession of rocks, from the oldest to the more recent, that are found on earth. The geologic column of Texas includes all rock divisions known to be present in the state. Geologists have determined that much of Texas is covered by rocks formed 65 to 135 million years ago during the Cretaceous period at the end of the Mesozoic Age. During this period, Texas was covered by an enlarged Gulf of Mexico.
In Texas, the Cretaceous Period has two divisions, known as the Lower
Cretaceous and Upper Cretaceous. Lower Cretaceous rocks blanket the entire
half of the state, while Upper Cretaceous rocks are found in a band from
the Red River southward to San Antonio and westward to Big Bend National
Park. Many formation names are applied to describe the complex picture
of Texas' Cretaceous rocks. The Lower Cretaceous portion is divided into
Washita, Fredricksburg, and Trinity groups. Upper Cretaceous rocks are
assembled into Navarro, Taylor, Austin, and Eagle Ford groups."
http://www.uwgb.edu/DutchS/StateGeolMaps/TexasGMap.HTM
My sincere appreciation to the following, that have helped me so much in understanding, identifying, and sharing, in the fascinating world of fossils; Lance Hall, Frank Holterhoff, Kelly Irwin, Earl Manning, Jimmy Matlock, and George Phillips.
