J. U. Dahyns Sf E. Greenly — Felsitic Slates of Snoivdon. 541 



Hector, J. 1885. "Note ou Geological Structure of the Canterbury Mountains " : 



Trans. N.Z. Inst., xvii, pp. 337-340. 

 Hector, J. 1892. " Index to Fossiliferous Localities in New Zealand" : Explor. 



Rep., 1890-91, pp. 120-178 (see pp. 155, 162). 

 HuTTON, F. W. 1 877. " Report on the Geology m the North-East portion of the 



South Island, from Cook Straits to the Rakaia": Explor. Rep., 1873-74, 



pp. 27-58, map and 3 pis. of sections (see p. 33). 

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Geol. Soc, xli, pp. 191-220 (see p.' 201). 

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Coast District, South Island" :■, E:^plor. Rep., 1873-74, pp. 74-115 (see 



p. 80. On p. 101 is recorded "a large Bentalium ... 4 inches long 



. . . ^ an inch thick . . . striated longitudinally." On p. 110 is 



mentioned "a small Bentalium.'''' See also pp. 116, 117). 

 M'Kay, A. 1878. " Report on the Wairoa and Dun Mountain Districts " : Explor. 



Rep., 1877-78, pp. 119-159, map and sections (see pp. 132, 137, 158). 

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Explor. Rep., 1878-79, pp. 97-121 (seep. 117). 

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Counties": Explor. Rep., 1879-80, pp. 83-107. 

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pis. xviii-xxii. (Bibliography on p. 367.) 

 Ulrich, E. 0. 1904. "Fossils and Age of the Yakutat Formation. Description 



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iv, pp. 125-146, pis. xi-xxi (see p. 132 and pi. xi). 



III. — On the probable Pelean Origin of the Felsitic Slates 

 OF Snowdon, and their Metamorphism. 



By J. R. Dakyns, M.A., and Edward Greenly, F.G.S. 



Part I : By J. E. Dakyns, M.A. 



THEEE are several kinds of acid volcanic rocks in Wales. In the 

 neighbourhood of Snowdon there are at least five kinds, as 

 follows : — 



1. There are undoubted lavas, showing lines of viscous flow and 

 sometimes vesicular, and weathering into cubical blocks. Such may 

 be seen on Crib Goch and on Crib Yddysgl, on Cerrig Cochion, and 

 elsewhere. These rocks are rarely cleaved. 



2. There are rocks like the last as to fracture and mode of 

 weathering, but which are neither viscous nor vesicular. They are 

 probably masses of felsitic dust or mud. Such may be seen in 

 Cwm Llan. 



3. There are also massive felstones, rudely cleaved, such as form 

 Moel Meirch and Clogwyn Llwyd. 



4. There are the so-called ashes of various kinds, usually well- 

 bedded and often highly cleaved. 



5. Lastly, there are highly cleaved felsitic rocks, which show no 

 lines of viscous flow, are generally unbedded, and which are in 

 many places fragmentary. They are markedly different from the 

 undoubted uncleaved lavas with which they are in some places 

 associated ; and though not readily to be distinguished from cleaved 

 lavas they are so often obviously fragmentary that I cannot but 

 consider them to be mainly of clastic origin. 



With reference to these rocks Mr. Greenly wrote to me im- 

 mediately after the meeting of the British Association at Southport 



