84 HOT SPKINGS, ARKANSAS. 



and resembles chert in its general appearance, although, as will be 

 shown later, this appearance is purely a superficial one and the mate- 

 rial differs markedly from chert in its origin and composition. 

 Although brittle and lacking the toughness of chert, it was exten- 

 sively used by the Indians, who quarried it by building fires upon the 

 outcrops until the stones were heated and then quenching the fire with 

 water, thus chilling the rock and causing it to split and spall into frag- 

 ments which were easily removed. In this condition it was readily 

 chipped by the use of round stone hammers, great quantities of which 

 have been found by the early settlers and which the writer has seen at 

 some of the more remote quarries. The rock is finely jointed, and in 

 quarry faces this jointing is more conspicuous than the bedding planes. 

 These phenomena may be well observed in almost any of the excava- 

 tions seen along the main street above the Government reservation. 

 The liner-grained material seldom forms good outcrops, because of this 

 jointing and also because the rock contains a small amount of water, 

 which, when frozen during the frosts of winter, shatters the stone and 

 covers the outcrop with fine debris. This debris is extensively used 

 as a road material, and wherever applied forms a most excellent 

 surface. 



The novaculite formation is from 500 to 600 feet in thickness, which 

 includes some flinty shales, some soft shales, and some sandstones. The 

 novaculites proper are prominent members of this formation and occur 

 in beds a few inches to 12. or 15 feet thick. When these beds are less 

 than 1 inches thick the rocks lose the novaculite character, and are 

 more like flinty shales. When examined under the microscope the 

 rock is found to present a very uniform appearance, and to consist 

 of extremely minute interlocking grains of cryptocrystalline silica. 

 Chemical tests show that this silica is quartz and not amorphous silica. 

 Thin sections also disclose the presence of numerous cavities in the rock 

 quarried for whetstones. These cavities have been found to present a 

 rhomboidal outline, and they correspond in form and position to included 

 patches of calcite found in the same rock where the bed passes beneath 

 the creek levels. It has been assumed that these cavities are formed 

 by the dissolution and removal of the calcite, and as the material from 

 beneath the water level is of slight value as a whetstone, it has been 

 reasoned that the abrasive qualities of the Arkansas stone are due to 

 the presence of these calcite cavities. The origin of the rock has been 

 the subject of considerable speculation from the earliest times to the 

 present. It has been commonly asserted that it is a very fine-grained 

 sandstone, which has been indurated and altered by hot-spring action. 

 This explanation is not adequate, however, since the same beds are 

 exposed on the flanks of the Ouachita Mountain system for a total 

 length of several hundred miles. Moreover, the character of the grains 

 does not permit of the assumption that they were originally rounded 

 and that the spaces between have been filled by secondary deposition 

 of silica, as is commonly the case with many quartzites. The writer's 

 belief is that the evidence supports the opinion that the rocks were 

 formed as a chemical precipitate in the deep seas of a Silurian ocean, 

 and that comparatively little alteration beyond induration has taken 

 place. Such a theory seems to accord very well with the chemical and 

 physical nature of the rock and with the facts now known in regard to 

 the origin of some of the early geological sediments. 



