Vol, 54.] CARBONIFEROUS LIMESTONE NEAR LLAKDTJDNG. 387 



The following analysis was kindly made for me by Mr. H. Eairrie 

 at Dr. George Tate's College of Chemistry, Liverpool : — 



Per cent. 



Lime 2778 



Magnesia 22-83 



Iron protoxide (FeO) ' "48 



Iron sesquioside (FcoOg) *59 



Silica ". -40 



Water j69 



Carbon dioxide 47*23 



10000 



From the above the percentage of the carbonates is seen to be : — 



Carbonate of lime 4960 



„ magnesia 47"95 



The original bedding is preserved, but there is little or no shale 

 between the beds. Fossils seldom occur, and then only in the 

 upper surface of the beds, but at the bottom of the wooden steps 

 down to the beach, just beyond the Pier, are two or three beds of 

 limestone, interstratified with the dolomite, containing Syringopora 

 ramulosa and the stems of encrinites. These are some of the 

 lowest visible beds, and they dip 25° W.N.W., but those described 

 as occurring at Chapel Walks must be under them. On the high 

 ground above the Happy Valley the dip is 18° W., and on the Old 

 Road, near Kenrick's Museum, it varies from 26° to 22°, and 

 finally is 16° W., where it is covered by the succeeding subdivision 



The thickness of the Lower Brown Limestone is about 400 feet 

 between the Old Road and the Happy Valley, and it is succeeded 

 by a grey shale and black limestone at the base of the Middle 

 White Limestone. The shale is a well-defined horizon separating 

 the two subdivisions, but farther south-west the dolomitization of the 

 limestone has ascended and altered the lower beds of Middle White 

 Limestone, as may be seen about Pen Morfa Lodge, and along the 

 Old Road from Llandudno to Roft Fach, where the shale is absent 

 and the dolomite and limestone alternate, the beds often changing 

 horizontally from one rock into the other. 



The Lower Brown Limestone has been extensively converted into 

 dolomite after its original deposition. This is proved by the 

 irregular horizon of the dolomitic rock about its upper limits, and 

 its occurrence in lenticular masses in the two overlying subdivisions. 

 It forms the fiilling of faults and string-courses in the limestone, 

 and has evidently been altered long after the deposition and dis- 

 location of the strata. The dolomite is intimately connected with 

 the mineral veins, for on ascending from Llandudno by the Old 

 Road that rock on the south-west extends nearly | mile farther 

 than on the north-east side, and suggests the occurrence of a con- 

 siderable rather than an insignificant fault. The upthrow side of 

 the fault is exposed south of a cottage at Roft Fach, where the 

 striated surface hades 58° N., but the fault does not extend much 

 farther up the hill where the limestone is continuously exposed. 



