The slates from the Bundenbach area have been used for building purposes since ancient times. While quarrying, fossils were occasionally found and set aside due to their value to collectors. There were as many as 600 small pits where slate was collected. Today only the Bundenbach quarry remains open. The slates date to the Early Devonian (396-390 million years ago). They were deposited during the Early Esmian to Late Pragian Ages. The main belt of deposits runs about 100 miles from southeast to northwest. The thickest deposited sediments are estimated at 4,400 feet tapering to only about 220 feet at the south end. The deposition appears to have been a series of subsiding basins separated by swells with reduced and partly sandy iron-rich sediments. Often fossils are covered by a surface layer of pyrite. When the fossils were buried quickly in an anoxic (oxygen free) environment the conditions necessary for pyritization was more likely to occur in these iron-rich sediments. These pyritized specimens are highly sought after by collectors. Retail price for a Urasterella asperula of this quality is about $700.0 to $800.00. Dimensions: 7-3/4" x 8-1/2" x 5/8"