96 Correspondence — Mr. Charles Callmvay. 



the action of tlie atmospheric agents, and, above al], by the lichens. 

 This is also the reason why the smaller islands and the lower 

 portions of the larger ones, as Professor Milne remarks, are of a 

 whitish colour. As long as the waves hinder the lichens from at- 

 taching themselves to the rOck, it preserves its scratched and 

 polished surface, but when elevated a few feet above the sea-level, 

 it soon becomes rough and dark. In places that were sheltered from 

 the action of the glacier-ice, the rock is never polished and scratched, 

 though on our coasts these places are usually the most exposed to the 

 action of the waves and to coast-ice. 



Geological Survey Office, Gr, LiNNAESSON. 



Stockholm, November ZOth. 



DEVONIAN GEOLOGY. 



Sir, — One is scarcely surprised to find that the papers of Messrs. 

 H. B. Woodward and C. Eeade, in the last October Number of the 

 Geological Magazine, afford such strong support to the masterly 

 interpretation of the Geology of Devonshire given to the Geological 

 Society by the late Professor Jukes and published at his own 

 expense. 



Professor Jukes's knowledge of the Irish rocks with which he 

 classed those of Devonshire, together with his powerful and practised 

 ability for field observation, entitled his opinions to more considera- 

 tion than at the time they appeared to receive. 



Now that he is gone, it is gratifying to see his ' able outline ' 

 being ably filled in with careful details, and should the further 

 revision still bear out his views, this will show how apt was a 

 remark he often made regarding puzzles in field geology/ "Put all 

 the evidence down, and it will explain itself." 



"Wijjiyan, Mv. 19th, 1877. Benwyan. 



THE VOLCANIC ROCKS OF SHROPSHIRE. 



SiK, — Mr. S. Allport, in his valuable paper " On Certain Ancient 

 Devitrified Pitchstones and Perlites from the Lower Silurian District 

 of Shropshire " (Quart. Journ. Geol. Soc, vol. xxxiii. part 3, August, 

 1877, p. 449), read May 23rd, 1877, announced the discovery of the 

 bedded character of the so-called " Greenstone " of the Wrekin. The 

 same fact was communicated by me to the Society on March 21st, 

 1877, in my paper " On a new area of Upper Cambrian Eocks in 

 South Shropshire," which however did not appear until the publica- 

 tion of part 4 of the Quart. Journ. Geol. Soc, in November, 1877, 

 p. 652. The value of this discovery will be seen when it is remem- 

 bered that these " Lower Silurian " rocks are really Cambrian, some 

 of them clearly as ancient as the Lingula Flags, if not Menevian, 

 and that tliey rest upon the bedded volcmiic series unconformably. I 

 am working out the details of this great formation, but shall not 

 publish until I have collected further materials. 



Chaeles Callaway. 



"Wellington, Salop, Dec. llih, 1877. 



