58 Mr. C. Lapworth on the Geological 



Spain. — Rocks of Llandovery age occur also in the southern 

 districts of the Peninsula. Among the so-called Lower Silu- 

 rian fossils enumerated by De Verneuil and Barrande as 

 present in the Lower Palasozoic strata of Almaden and the 

 Sierra Morena are found * 



Monograptus spiralis, Geinitz. Monograptus priodon, Bronn. 

 Halli, Bail'. Diplograptus palmeus, Barr. 



America. — Throughout the United States and Canada the 

 Llandovery strata consist almost wholly of coarse sandy non- 

 fossiliferous beds or of calcareous rocks abounding in Brachio- 

 poda, but destitute of Graptolites. The Clinton beds, which 

 may be roughly paralleled with our Tarannon Shales, afford 

 the peculiar American forms 



Monograptus clintonensis, Hall. Retiolites venosus, Hall. 



Salopian (or Wenlock and Lower Ludlow) Formation. 



The great Mudstone or Salopian formation of Shropshire 

 is more or less graptolitiferous throughout. In a few locali- 

 ties its basal strata afford Rhabdophora in remarkable abun- 

 dance. As we ascend the succession they gradually diminish 

 in numbers, as a general rule. To this, however, there are 

 exceptions. One of the most noticeable is that at the base of 

 the Lower Ludlow, where, more especially in Hereford and 

 Radnor, some of the beds are crowded with Graptolites. They 

 are, however, of but few species, and belong to a single genus 

 only. About the horizon of the Aymestry Limestone they 

 vanish altogether ; but whether this is due to the change in 

 the composition of the strata, which here begins to take on a 

 coarse sandy character, or whether it is owing to rapid ex- 

 tinction of the order, it is as yet impossible to determine. 



(a) Zone of Cyrtograptus Murchisoni, Carr. 



Wales. — The base of the Wenlock or Salopian series of the 

 neighbourhood of Builth is formed of a few feet of calcareo- 

 carbonaceous shales, crowded with fairly preserved Rhabdo- 

 phora, among which the beautiful species Cyrtograptus Mur- 

 chisoni, Carr., is especially conspicuous. It is associated 

 with 



Monograptus priodon, Bronn. Monograptus colonus, Barr. 



Halli, Barr. Retiolites Geinitzianus, Barr. 



Tomerinus, Nich. 



The same zone is probably present in the shales at the base 

 of the Wenlock, on the banks of the Onny, near Plowden, 



* De Verneuil et Barr. Bull. Geol. Soc. France, 1855, p. 064. 



