Chap. III.] 
LLANDEILO EOCKS IN SHROPSHIKE. 
49 
district, and hence termed 0. plumbea (f. 1). Besides this, there are 
the well-known fossils Orthis alata and 0. calligramma (Sil. Syst.) ; and 
these are accompanied by Redonia and Ribeiria (f. 2, 3) ; whilst the 
several species of Orthocerata, to one of which Mr. Salter assigned, at 
my request, the name of 0. Avelinii (f. 4), were no less important aug- 
mentations of our knowledge. Again, among those characteristic Silurian 
animals the Graptolites, besides some previously recognized species (Di- 
plograpsus pristis and Didymograpsus Murchisonii), we find both the diver- 
gent and reflexed varieties of the Didymograpsus geminus, a well-known 
Silurian species in Sweden and Norway. There is also a Fenestella, a 
Polyzoon differing essentially from the Dictyonema above mentioned 
(p. 46), and of an expanded cup-like form. There are also other fossils. 
Other species, with some of the above-mentioned forms, are found in 
the equivalent strata in those parts of Wales to which attention will be 
soon directed. 
On the western flank of the Stiper Stones, this the lowest part of the 
Llandeilo formation contains many interstratified bands of igneous ma- 
terials, being what were termed by me ' volcanic grit ' when this tract was 
first described, but now more currently known under the term of ' ashes ' *. 
Several striking courses of such rocks are exhibited at Cefn y Gwynlle and 
various other spots f . These, with bosses of igneous rocks of intrusive 
character, the chief mass of which is seen in the Corndon Mountain, as re- 
presented in the annexed drawing, will be described when the succession of 
Lower Silurian tract west op the Stiper Stones (Shelve, &c). The Corndon 
Mountain in the distance towards the North. 
(From Sil. Syst. p. 271.) 
Lower Silurian rocks, interstratified with contemporaneous ashes and lavas, and tra- 
versed by eruptive rocks. 
organic life in the Llandeilo and Caradoc formations of various districts 
shall have been explained. Again, this district is eminently metalliferous, 
* These are the " green slates " of some German mineralogists. For the German synonyms of the 
igneous rocks of Wales and the Silurian Eegion, see the Appendix (C). 
t See Map of Geol. Survey, Sheet 60. 
