I ni 



N 



•-« 



■v. 



■ 











AND SHROPSHIRE. 



173 



igneous rocks, 



Uppfb 



Galleby. 



The word contemporaneous, applied to 

 means, that, according to their nature, they were poured 

 out as lavas, or showered abroad as ashes, in general Wall-case 4« 

 terms, contemporaneously with the formation of the strata 

 amid which they immediately lie. The ashes are truly stra- 

 tified deposits, and the lava-flows may also in a measure be 

 spoken of as strata in the sense that they are inter -bedded. 

 The eruptive rocks of the sections are of two kinds : 



1st. FelSpathic and quartz porphyries and syenite. 

 2nd. Greenstones. 



The first are coloured deep scarlet (Sections a, a, and s). 

 Their nature will be seen by referring to the specimens in 



Case 



Numbers corresponding to those on the specimens 



which the specimens ivere derived. 

 117. — Syenite. See Section 4. 



of rock ft 



124, 184, and 185. 



Q 



porphyry. See Sections 



1 and 4. 



These and others of like nature occur in large masses, 

 altering the strata with which they are in contact all round. 

 (Section 4, and specimens 186 to 191.) In the sections 

 (no. 1 and 4) four of these masses break up among the 

 Cambrian, and three among the Lower Silurian rocks. Many 

 others occur in Wales not crossed by any of the sections. 

 Their structure, mode of occurrence, and the effects they 

 produce, show that those parts of them we now see, being 



feat is to say, that the surf 



•fi 



if 



have since been removed by denudation, or in other words 

 by the gradual stripping away of such overlying masses by 

 atmospheric and other agencies. 



The greenstones are coloured deep crimson, and appear in 

 all the sections, breaking indiscriminately through the Lower 

 Silurian strata, and sometimes through the associated inter- 



bedded igneous rocks. 



>//< 



and hornblende, sometimes somewhat amorphous or indis- 

 tinctly crystallized (specimens 152, 164, &cA at other times 



