File:The Quarterly journal of the Geological Society of London (13937262342).jpg

ON

 THE 
 NORTHERN 
 SLOPES 
 OP 
 CADER 
 IDRIS. 
 425 
 

or

 more 
 across. 
 In 
 thoir 
 cracked 
 and 
 scoriaceous 
 interior 
 calcite 
 has 
 

developed

 freely, 
 so 
 much 
 so 
 as 
 to 
 suggest 
 at 
 first 
 the 
 presence 
 of 
 

ejected

 limestone 
 blocks. 
 After 
 boiling 
 this 
 crystalline 
 alteration- 
 

product

 in 
 hydrochloric 
 acid, 
 the 
 residue 
 yields 
 little 
 of 
 interest, 
 

quartz

 and 
 a 
 few 
 brown 
 flakes 
 of 
 mica 
 being 
 the 
 only 
 identifiable 
 

minerals.

Prof.

 Ramsay 
 * 
 has 
 commented 
 on 
 the 
 difficulty 
 of 
 distinguishing 
 

between

 the 
 compacter 
 intrusive 
 sheets, 
 themselves 
 often 
 scoriaceous, 
 

and

 the 
 soft 
 grey-green 
 ash-beds. 
 On 
 the 
 broken 
 slopes 
 between 
 

Llyn-y-Gafr

 and 
 Llyn-y-Gader 
 the 
 cleavage 
 of 
 the 
 district 
 has 
 affected 
 

some

 of 
 the 
 igneous 
 layers, 
 while 
 every 
 crack 
 and 
 hollow 
 is 
 filled 
 

with

 secondary 
 calcite. 
 Hence 
 the 
 rocks 
 afford, 
 when 
 considered 
 in 
 

the

 laboratory, 
 excellent 
 hand-specimens 
 of 
 " 
 Schalstein 
 ; 
 " 
 but 
 to 
 

designate

 them 
 by 
 such 
 a 
 name 
 is 
 to 
 admit 
 that 
 we 
 are 
 baffled 
 in 
 

the

 field. 
 

Some

 of 
 the 
 undoubted 
 ash-beds, 
 even 
 when 
 soft 
 and 
 calcareous, 
 

are

 divided 
 by 
 jointing 
 into 
 spike-like 
 columns 
 ; 
 while 
 the 
 compacter 
 

and

 more 
 metamorphosed 
 ashes 
 at 
 the 
 base 
 of 
 the 
 cliff 
 of 
 Mynydd 
 

Fig.

 2. 
 — 
 Beds 
 beneath 
 the 
 Eurite 
 on 
 Mynydd 
 Moel. 
 

1.

 Black 
 Slates, 
 with 
 cleavage 
 practically 
 coincident 
 with 
 bedding. 
 

2.

 Altered 
 flinty 
 slates, 
 with 
 well-marked 
 bedding. 
 

3.

 Greenish 
 softer 
 laver. 
 

4.

 Bedded 
 Ash, 
 altered 
 and 
 jointed 
 into 
 columns, 
 

5.

 The 
 Massive 
 Eurite. 
 

Moel

 imitate 
 closely 
 the 
 columnar 
 eurite 
 of 
 the 
 wall 
 (fig. 
 2). 
 The 
 fine 
 

layers

 of 
 the 
 bedding, 
 however, 
 frequently 
 weather 
 out, 
 and 
 give 
 a 
 

clue

 to 
 the 
 origin 
 of 
 the 
 rock 
 ; 
 while 
 microscopic 
 examination 
 removes 
 

many

 of 
 the 
 difficulties 
 presented 
 by 
 the 
 porcellaneous 
 varieties 
 f 
 . 
 

 Memoirs 
 of 
 theGeol. 
 Surv. 
 of 
 Gt. 
 Britain, 
 vol. 
 iii. 
 2nd 
 edition, 
 p. 
 31. 
 

t

 Mr. 
 J. 
 Clifton 
 Ward 
 discussed 
 the 
 microscopic 
 characters 
 of 
 somewhat 
 

similar

 ashes 
 in 
 his 
 paper 
 on 
 the 
 " 
 Structure 
 of 
 Ancient 
 and 
 Modern 
 Volcanic 
 

Rocks,"

 Quart. 
 Journ. 
 Geol. 
 Soc. 
 vol. 
 xxxi. 
 (1875) 
 p.