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Of fossils of this genus, which is very characteristic of the Lower Silurian, I shall again speak in the sequel. b. Though not always recognised as a separate subdivision of the Wenlock, the Woolhope beds, which underlie the Wenlock shale, are of great importance.
The formations below the Arenig or Stiper-stones group are treated of in the next chapter, when the "Primordial" or Cambrian group is described. LUDLOW FORMATION: a. Upper Ludlow beds: 780. b. Lower Ludlow beds: 1,050. WENLOCK FORMATION: a. Wenlock limestone and shale and b. Woolhope limestone and shale, and Denbighshire grits: above 4,000. Lower Llandovery: 600-1,000.
Such facts may be useful in warning us not to assume too hastily that the point which our retrospect may have reached at the present moment can be regarded as fixing the date of the first introduction of any one class of beings upon the earth. We next come to the Wenlock formation, which has been divided into Wenlock limestone, Wenlock shale, and Woolhope limestone and Denbighshire grits. a.
It contains the usual Wenlock fossils, but with the addition of some common in the uppermost Ludlow rock, such as Chonetes lata and Bellerophon trilobatus. The latter attains in the Woolhope beds an unusual size for the species, the specimens being sometimes twice as large as those found in the Wenlock limestone.
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