1895.] NATURAL SCIENCES OF PHILADELPHIA. 151 



The sea then had free access to this portion of the shore, at least, 

 and the clear marine water meeting- the mud-laden fresh water of 

 creeks and rivers caused the latter to drop their burdens with the 

 result of a deposition of a great depth of laminated clays and sands,™ 

 Marine and fresh, or brackish water conditions alternately prevailed. 

 The subsideuce continued and the marine conditions becoming 

 stronger many of the marine forms of life gradually crept up aloug 

 the shore and we have a solid eight feet of limestone. A slight 

 change takes place and two feet of sand are laid down, again to be 

 succeeded by another bed of limestone of the same character as 

 before, this time ten feet in thickness. 



Following this upper limestone we have 120 feet of clay and 

 finally 30 feet of sand with calcareous boulders and a few fossils and 

 then another change takes place. The old channel with its sands, 

 clays and limestones is completely obliterated and a shallow, brackish 

 water condition of affairs takes place, covering the whole area from 

 west to east with a totally different set of deposits. These form the 

 great liguitic series of this region. 



The changes that ushered in the liguitic stage brought about the 

 final destruction of the glauconitic sandy portion of the upper cre- 

 taceous, completed the isolation of the cretaceous islands and laid 

 down great beds of sand along the whole coast. Owiug to ex- 

 tensive overlapping of the newer members of the series, the base of 

 these beds is seldom seen but wherever sufficiently deep exposures 

 occur the basal portion of these liguitic deposits are found to be 

 made up of coarse bluish-gray, to gray, sand with occasional in- 

 terstratified strata of indurated sand or soft sandstone, more or less 

 calcareous, and at wide intervals these deposits are interstratified 

 with thin strata of laminated clay. In the Brazos River section 

 these deposits have a thickness of about 300 feet, but they become 

 thinner as they extend eastward and westward from this line. In 

 the northeastern portion of the State these sands rest directly upon 

 the cretaceous and are very much thinner and have a thickness of 

 probably not more than 50 feet. . 



The conditions brought about by these changes appear to have 

 been inimical to animal life, or at least to the preservation of its 

 remains. Nowhere within the whole region has a solitary individual 



79 Geikie's Text Book of Geology, Second edition, p. 355. 



