PETROLOGY. 25 



men, the sandstone, however soft, can always be trimmed into a solid 

 block. For this reason the one is useless, and the other useful, for 

 building purposes. 



In the main, the sand-rock is a pure, micaceous, slightly ferrugi- 

 nous, and sometimes felspathic, sand as to its basis. It is of sugary 

 texture, and without jointing or other divisional planes. Pale ochre 

 colours generally prevail ; but a banded coloration is more com- 

 mon, in which the former are associated with pale blue greys, cho- 

 colate browns and pale purplish tints. Sometimes the rock weathers 

 white and sometimes pepper-and-salt colour. Reddish brown clays 

 are freely interstratified, and grey clays and loams are very pre- 

 valent in its uppermost layers. It is said by Mr. Medlicott to 

 resemble the Swiss molasse in texture and composition. A charac- 

 teristic feature of the sand-rock is the presence of numerous nodular 

 layers, apparently of the nature of concretions. They are sometimes 

 massed into a thin tabular layer, and they vary in thickness from a 

 few inches up to two feet. Their surfaces are wavy and mammillated, 

 owing to the concretionary action round different centres interfering 

 and mingling the one with another. These layers become so hard as 

 to ring unmistakeably under the hammer, and to stand out in relief 

 in the river-bed and scarp. They are sometimes broken up into dis- 

 tinct masses of remarkably spherical shapes, like the concretions in 

 the lower Kelloway rock of the north of England. Not unfrequently 

 they appear in grotesque forms like flints. Occasionally, as in the 

 Pelani R., they become so like flattened pebbles, in their distinctness 

 from the rock matrix, that one may be easily deceived by them. In the 

 Rdmganga R., among Nahan sandstones, some two or three miles from 

 Kalagarh, there are similar concretions which I may notice here. 

 They are a foot or more in diameter, and of a different colour to the 

 rest of the rock. Their appearance is, in fact, that of stray boulders 

 scattered in a finer matrix. I was fairly misled by them at first ; 

 but a search for scratchings and groovings proved that the bedding 

 of the supposed boulders always coincided with the bedding of the 

 sandstone in which they lay. In every one of thirty or forty cases 



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