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<br />2394 <br /> <br />The Brushy Basin Shale Member consists of variegated <br /> <br /> <br />. mudstone containing considerable amounts of bentonitic <br /> <br /> <br />clay, interbedded with siltstone and siliceous sandstone. <br /> <br />The mudstone and siltstone units are predominately pinkish <br /> <br />gray (5YRB/l) to light greenish gray (5G8/1). The <br /> <br />bentonitic clay probably is derived from volcanic material <br /> <br />and causes the mudstone to weather to a characteristic <br /> <br />frothy surface. Ekren and Houser (1959a, p. 192) note <br /> <br />that the "* * * distinctive frothy appearance is a result <br /> <br />of swelling and subsequent drying of the contained bentonite. <br /> <br />Swelling muds are not present in the lower members of the <br /> <br /> <br />Morrison or i~he Burro canyon formation." <br /> <br /> <br />The sandstone units are white, yellowish gray (5YB/l). <br /> <br />and light greenish gray (5GB/I) and are composed of very <br /> <br /> <br />. fine- to fine-grained sub rounded to rounded clear and <br /> <br />frosted quartz. Ekren and Houser (1959a, p. 192) report <br /> <br />one 20-foot crossbedded conglomeratic sandstone, although <br /> <br />conglomerate and conglomeratic sandstone are not common. <br /> <br />Where the member is capped by more resistant Burro Canyon <br /> <br />and Dakota Sandstones, it weathers to a steep multicolored <br /> <br />slope with small ledges of sandstone. <br /> <br />. <br /> <br />N- <br />