210 Mr. AiYii-i^ on the Wrekl ft, and on the 



larger ones, very much compressed. These cells are lined with 

 minute hexahedral prisms of quartz mixed vv^itli a greenish-yellow 

 earthy matter, which is perhaps decomposed actynolite. This rock 

 is penetrated by veins containing qu.irtz, flesh-red jasper, and chalce- 

 dony, the latter of which fills all the cells of the adjdcent rock. 



An analogous variety is found on the top of the Wrekin, in which, 

 however, the compression of the cells has proceeded so far as to 

 bring their sides into actual contact, thus giving the rock a waved and 

 striped appearance. 



2. Greenstone rocks. 



These for the most part appear to lie under the claystone rocks. 

 Their essential component ingredients are dull-green hornblende and 

 greenish or reddish felspar. They all affect the magnetic needle, 

 some of them in a very remarkable degree. They are more easy cf 

 decomposition than the felspar rocks just mentioned, and, in conse- 

 quence, the respective place of each may be easily distinguished in 

 the hills where they both occur, by the bare craggy surface of the 

 one, and the smooth depressed verdant surface of the other. 



When the component parts of the greenstone are distinct, and the 

 felspar has its foliated crystalline structure, the only foreign ingredi- 

 ent which I have observed in the rock, is magnetic pyrites, in small 

 grains. But where the hornblende and felspar are more intimately 

 mixed, the rock usually becomes amygdaloidal, and contains globular 

 concretions of felspar, quartz, calcareous spar, hsematite, zeolite, and 

 actynolite. Of these amygdaloids there is one of remarkable beauty, 

 (described by Dr. Townson in the tract already referred to), and 

 forming large masses on Caer Caradoc, but which has not yet found 

 a place in the works of systematic mineralogists. It consists of a 

 dull earthy basis, formed by an intimate mixture of dark bluish green 

 hornblende, with flefh-red felspar, inclosing globular concretions of 



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