948 Notes, principally Geological, from [No. 130. 



of discovering the line of termination, I spent several hours in searching 

 the beds of streams, and visiting the quarries in the neighbourhood, and 

 at last discovered it in the bed of a nullah, about three hundred yards 

 south of the village : here, after clearing away the gravel and detritus com- 

 posing the bed, I distinctly saw the trap overlying the sandstone, and 

 penetrating some of the numerous fissures that cleave the latter. I 

 had anticipated this fact from the circumstance of the little disturbance 

 in the latter rock, which occurs in tabular horizontal masses, having 

 a rhomboidal shape from being intersected by fissures with a varied 

 direction, but generally N. 65 W., crossed by others trending S. 20 W. 

 Where the trap had penetrated them, I did not find the two rocks ad- 

 herent, or passing into each other ; but perfectly distinct and separate, 

 and occasionally a thin calcareous seam intervening. Both the trap 

 and sandstone seem to be slightly altered by contact, the former be- 

 coming less crystalline and more earthy, but often extremely tough, and 

 splitting into small fragments, with numerous microscopic fissures in- 

 tersecting its structure. The colour of the sandstone, from a few lines 

 to several inches distant from the contact, is generally reddish, passing 

 into a deep reddish brown. There was no appearance of semi-fusion, 

 or intermixture, nor entangled masses of sandstone in the trap, a cir- 

 cumstance coinciding with the observations of Lord Greenock, in his 

 account of the phenomena displayed by the igneous rocks in the neigh- 

 bourhood of Edinburgh, in their relations to the secondary rocks : nor 

 did I observe any solidification in the former, as noticed by Professor 

 Hausmann, in the sandstone altered by heat near the blast furnaces at 

 the Steinrennerhutte in the Harz : on the contrary it was of a looser 

 texture than ordinary. In structure, from a loose and variegated grit, 

 it approaches a compact quartz rock, containing disseminated portions 

 of decomposed felspar, which falling out, leave a number of minute 

 oval cavities. This stone is much used in building by the villagers in 

 preference to the trap. I saw no veins penetrating the sandstone ; 

 pegmatite occurs in scattered blocks : the situs of this rock cannot be 

 far distant, judging from the sharpness of the angles of these fragments. 

 Proceeding in an easterly directions towards Talicota, the trap forma- 



... tion extends to the village of Mudkeysur, three 



I rom Alcopa to Talicota. ° # ' 



coss from Alcopa, when it is succeeded by 



bluish grey compact limestone, which I first observed in the bed of 



