192 PETRIFIED SHELLS, FOUND IN THE 



in various stages of decomposition. It is owing to the difficulty with 

 which the roots of trees penetrate this rock, that they are so rare on its 

 surface, and never grow to any size ; yet this circumstance does not pre- 

 vent the Andropogon contortum and nardus from growing in the most 

 luxuriant manner, which sufficiently proves the fertility of the soil. 



On ascending from the Tapti, I observed in a nullah, a group of 

 basaltic columns, one of which was two feet in diameter, and six sided. 

 When near the summit of the flat table land of J^i7Zflf>i, I entered on a pass, 

 formed on one side by a perpendicular section of the rock, from twenty- 

 five to thirty feet, and on the other, by a rapid descent of forty or fifty. 

 The lower part of the section, as well as the pathway, is composed of 

 the wacken, or indurated clay, of the kind I have before mentioned, 

 of about ten feet in thickness ; lying on it is a stratum of earthy 

 clay, of different degrees of induration and purity, twenty yards in 

 length, and of about two feet in thickness, containing great numbers 

 of entire and broken shells. This possesses all the characters of a 

 stratum, since the horizontal fissures are parallel, and are prolonged, 

 with a few interruptions, through the whole extent. The accompanying 

 sketch will serve to give a tolerably correct idea of the mode in which 

 the stratum appears to overlie the lower rock, and to have been depress- 

 ed by that which is superincumbent. The upper rock consists of about 

 fifteen feet in thickness of the nodular basalt, or wacken. The nuclei 

 being of all sizes. The vertical fissures, which are so remarkable in 

 trap rocks, are prolonged from both the upper and lower rocks into 

 the shelly stratum, although there is no intermixture of substance. 



The stratum is composed of a highly indurated clay, fusible before the 

 blowpipe into a fine black glass, and neither it nor the shells it contains, 

 effervesce in acids. The shells are, for the most part, flattened, and belong 



either 



