Post by 1dave on Nov 10, 2013 12:04:59 GMT -5
Christmas 1969 - Visiting Mom in Austin, I asked at a local rock shop, "Any interesting rocks around?"
"Yeah, (I wish I could remember his name) When they built the Ben White Blvd overpass above South Congress Ave, they used a blue clay full of pyrite coated ram's horn shells called Exogyra."
What a fun afternoon! My brothers had to come and drag me away for the Christmas Dinner!
I just googled the area. My how times have changed! Ben White went over Congress ave.
Now that has all been dug out and the roads reversed!
Wonder where all that fill went?
Where did it come from in the beginning?
Happy Hunting!
Dave
"Yeah, (I wish I could remember his name) When they built the Ben White Blvd overpass above South Congress Ave, they used a blue clay full of pyrite coated ram's horn shells called Exogyra."
What a fun afternoon! My brothers had to come and drag me away for the Christmas Dinner!
I just googled the area. My how times have changed! Ben White went over Congress ave.
Now that has all been dug out and the roads reversed!
Wonder where all that fill went?
Where did it come from in the beginning?
Annual Report of the Geological Survey of Texas
By Geological Survey of Texas -1889 Page 128
THE EXOQYRA ARIETINA CLAYS.
In Shoal Creek, at Barton Springs, near Round Rock, and other places in the vicinity of Austin, the Terebratula wacoensis horizon of the Washita limestone is surmounted by about eighty feet of unctuous laminated clays of a greenish blue color previous to long exposure to the elements, and dirty yellow afterwards. The lower half of these clays is filled with the small unique Exogyra ariztina or ram's horn oyster, which occurs in no other known horizon in the world.
. . .
THE SHOAL CREEK LIMESTONE.
In the western portion of the city of Austin, forming the rocky walls of the Shoal Creek Canyon, and for a few miles north and south, the uppermost strata of the Comanche series consist of beds of a peculiar crumbly limestone. This limestone is from forty to eighty feet thick, and of a yellow color, with many spots of red and pink.
It is stratified, and upon close examination it is seen to be made up of minute fragments of shell, which are rapidly losing their integrity by alteration either into a harder condition or by breaking down into a pulverulent powder, as in the case of the Caprina limestone before described. The red blotches have been attributed to several causes, to-wit: (1) The decomposition of iron pyrites; (2) the oxidation by heating of adjacent igneous material; and (3) the decomposition of contained volcanic ash and cinder which were deposited contemporaneously with it. This point has not been finally determined, however.
In places the Shoal Creek limestone is decomposing and crumbling, while everywhere it is much jointed and faulted. The fossils contained therein are interesting, but have been as yet but little studied. The top surface of this limestone has been corroded and waterworn, and deposited unconformably upon it can be seen the radically different sub-littoral unconsolidated clays of the basal Upper series.
This limestone makes a convenient building stone, but of no great commercial value. Its residual soil like that of the Caprina limestone, is of a rich dark red color, and covered with handsome timber growth, as seen at the Pease mansion in West Austin.
By Geological Survey of Texas -1889 Page 128
THE EXOQYRA ARIETINA CLAYS.
In Shoal Creek, at Barton Springs, near Round Rock, and other places in the vicinity of Austin, the Terebratula wacoensis horizon of the Washita limestone is surmounted by about eighty feet of unctuous laminated clays of a greenish blue color previous to long exposure to the elements, and dirty yellow afterwards. The lower half of these clays is filled with the small unique Exogyra ariztina or ram's horn oyster, which occurs in no other known horizon in the world.
. . .
THE SHOAL CREEK LIMESTONE.
In the western portion of the city of Austin, forming the rocky walls of the Shoal Creek Canyon, and for a few miles north and south, the uppermost strata of the Comanche series consist of beds of a peculiar crumbly limestone. This limestone is from forty to eighty feet thick, and of a yellow color, with many spots of red and pink.
It is stratified, and upon close examination it is seen to be made up of minute fragments of shell, which are rapidly losing their integrity by alteration either into a harder condition or by breaking down into a pulverulent powder, as in the case of the Caprina limestone before described. The red blotches have been attributed to several causes, to-wit: (1) The decomposition of iron pyrites; (2) the oxidation by heating of adjacent igneous material; and (3) the decomposition of contained volcanic ash and cinder which were deposited contemporaneously with it. This point has not been finally determined, however.
In places the Shoal Creek limestone is decomposing and crumbling, while everywhere it is much jointed and faulted. The fossils contained therein are interesting, but have been as yet but little studied. The top surface of this limestone has been corroded and waterworn, and deposited unconformably upon it can be seen the radically different sub-littoral unconsolidated clays of the basal Upper series.
This limestone makes a convenient building stone, but of no great commercial value. Its residual soil like that of the Caprina limestone, is of a rich dark red color, and covered with handsome timber growth, as seen at the Pease mansion in West Austin.
Colorado College Studies
books.google.com/books
1890 - Science
BY F. W. CRAG
The "ram's horn oyster," Exogyra arietina, F. Roemer, is the characteristic fossil of a column of sediments, the so-called Exogyra arietina marl, that in Hays, Travis and Williamson counties, Texas, consists mostly of caleareoargillaceous, and more or less ferruginous marl, and attains a thickness of sixty to eighty feet, occupying the interval between the top of the Washita limestone of Shumard and the base of the Shoal creek limestone of Hill. This column was recognized by Dr. Shumard as an important member of the Cretaceous section of Texas, and was named by him, the Exogyra arietina marl: and this name, either as it originally stood or under such slight variations of form as " the Exogyra arietina clay," "the Arietina marl," etc., has been used for it by most later writers. The same formation outcrops, with more or less interruption by faulting, mantling, etc., and with more or less variation in thickness and lithological character southwestward to the region of El Paso. Its detail in this direction being less known than that of its northward extension, will not here be discussed. From Austin to the Red river valley in Cooke and Grayson counties, the Arietina becomes, as Taff has shown, gradually reduced in thickness and decidedly more calcareous. For this calcareous northern phase of the Arietina which, in the Red river valley, occupies the entire interval between the summit of the Pawpaw clays of Hill and the base of the Dakota sandstone, Hill has recently proposed the name. Main-street limestone.*
The Main-street limestone, however, consists of two members. Its dual character has been independently determined in the field by the present writer. But the members that compose it were first recognized as terranes by Taff in his second Report on the Cretaceous Area North of the Colorado River,* who correlated the upper member with the Shoal creek (Vola) limestone.
books.google.com/books
1890 - Science
BY F. W. CRAG
The "ram's horn oyster," Exogyra arietina, F. Roemer, is the characteristic fossil of a column of sediments, the so-called Exogyra arietina marl, that in Hays, Travis and Williamson counties, Texas, consists mostly of caleareoargillaceous, and more or less ferruginous marl, and attains a thickness of sixty to eighty feet, occupying the interval between the top of the Washita limestone of Shumard and the base of the Shoal creek limestone of Hill. This column was recognized by Dr. Shumard as an important member of the Cretaceous section of Texas, and was named by him, the Exogyra arietina marl: and this name, either as it originally stood or under such slight variations of form as " the Exogyra arietina clay," "the Arietina marl," etc., has been used for it by most later writers. The same formation outcrops, with more or less interruption by faulting, mantling, etc., and with more or less variation in thickness and lithological character southwestward to the region of El Paso. Its detail in this direction being less known than that of its northward extension, will not here be discussed. From Austin to the Red river valley in Cooke and Grayson counties, the Arietina becomes, as Taff has shown, gradually reduced in thickness and decidedly more calcareous. For this calcareous northern phase of the Arietina which, in the Red river valley, occupies the entire interval between the summit of the Pawpaw clays of Hill and the base of the Dakota sandstone, Hill has recently proposed the name. Main-street limestone.*
The Main-street limestone, however, consists of two members. Its dual character has been independently determined in the field by the present writer. But the members that compose it were first recognized as terranes by Taff in his second Report on the Cretaceous Area North of the Colorado River,* who correlated the upper member with the Shoal creek (Vola) limestone.
Happy Hunting!
Dave
