FOREST OF WYRE AND TITTERSTONE CLEE HILL COAL FIELDS. 1065 



the Carboniferous Limestone Series of Clee Hill, and that this conclusion is confirmed 

 by all my subsequent work. Further, Dr Vaughan has suggested that the Upper 

 Avonian is represented on Clee Hill by the so-called Millstone Grit, and, as we shall 

 see, this is the case. 



The criteria by which the Pendleside Series is identified do not affect us, as the 

 series is absent from the Clee Hill. 



The Lanarkian and the higher subdivisions agree in possessing an Upper Car- 

 boniferous flora ; their separation from one another and the evidence for referring 

 the Clee Hill Measures to the Westphalian are discussed elsewhere (p. 1069). 



Meaning of the term Millstone Grit. — The relations of beds called Millstone Grit 

 to these palseontological divisions deserve attention. The term Millstone Grit has 

 no exact time-value. It has been applied to rocks of any age so long as they include 

 sandstones and lie intermediate between Carboniferous Limestone and Coal Measures. 

 The Millstone Grit of North Staffordshire, as is seen from the table, is almost wholly 

 of Lanarkian age. Its lowest beds yield a Lower Carboniferous flora, but a marked 

 " palseobotanical break" occurs a short distance above the base, and the higher beds 

 have a Lanarkian flora, i.e. an Upper Carboniferous flora from which certain species 

 that are abundant in the Westphalian (the Middle Coal Measures) are absent. 

 But the "Millstone Grit" of South Wales* includes (]) in all probability the 

 local equivalent of the Pendleside Series, presumably succeeded by (2) Lanarkian 

 strata, though the characteristic flora has not been discovered, and, at the top, 

 (3) rocks with an undoubtedly Westphalian flora. t It is certain, in fact, that the 

 equivalence of the " Millstone Grits " of different areas to one another cannot be 

 taken for granted ; in each area the exact age of the grit must be established by 

 independent evidence. 



The Cornbrook Sandstone (the Millstone Grit so called) of Clee Hill. 



Lithological Characters. — Sandstones with subordinate clays, shales, thin coals 

 (none workable), and rarely limestone. The series was evidently formed, on the 

 whole, under continental conditions ; but the limestone, which occurs within 

 300 feet of the base, is a marine deposit, containing the remains of sea-urchins, 

 bellerophons, etc. 



The sandstones have the characters usually associated with the name of Millstone 

 Grit. They are chiefly grey or white, but many are stained brown, or are cemented 

 up with limonite, or coloured buff, yellow, red, or green. As the colours of the 

 interbedded clays are similar and, in the latter case, are clearly original, it may be 

 inferred that those of the sandstones also are original. The rocks are fine- to coarse- 

 grained, and many are pebbly. The included pebbles, which are rarely more than 

 4 inches in diameter, and are generally much less, consist, in the great majority of 



* E. E. L. Dixon, in " The Country around Tenby and Pembroke," Mem. Geol. Surv., in preparation. 

 t Goode, Quart. Joum. Geol. Soc, vol. lxix, p. 252, 1913. 



