Hicks and Salter— Lingula Flags. 27 



met witL. in other counti-ies. When altered, as might be naturally 

 expected from the absorption of water, the specific gravity di- 

 minished, and might descend to 2-63 or 2-55. The internal columnar 

 structure and the peculiar concentric weathering of these rocks had 

 also been the subject of special study, and the results of the observa- 

 tions made, quite disprove the evidence of any so-called globular struc- 

 ture in these rock masses, but that the columnar, or so-called Basaltic 

 structure, was due merely to mechanical causes. The sedimentary 

 strata in contact were themselves frequently so altered by the con- 

 tact with the igneous rocks as to present in themselves a columnar 

 structure or jointing, in some cases quite or even more perfect than 

 in the igneous rock itself, and a bed of clay ironstone at Pouk Hill 

 was found, jointed into regxilar hexagonal columns by the heating 

 and subsequent cooling and contraction, due to the proximity of 

 the ig-neous rock, which formed the boss of Pouk Hill. Numerous 

 other examples could be cited. 



III. — Eesearches in the Lingula Flags iK South "Wales. Joint Report by- 

 Messrs. H. Hicks and J. "W". Salter, F.G.S, 



THE results of these researches have led to the discovery of an 

 entirely new British formation, and the authors propose a new 

 term for the group. The district of St. David's was anciently called 

 "Mensevia," and hence, following the example of our leading geolo- 

 gists, the authors propose the term "Meneevian" for the lower 

 division of the " Lingula Flags." Mr. Hicks described five sections 

 north and south of St. David's — the coast affording admirable views 

 of all the beds, from the central syenite through the olive, grey, 

 greenish, and purple beds of the Lower Cambrians, into the light 

 grey, black, and dark grey shales of the Mensevian group. Some 

 of the sections show a passage from this group into the " Ffestiniog 

 group " of Professor Sedgwick, which forms the upper portion of the 

 " Lingula Flags proper," and in Whitesand Bay (a fine bathing 

 strand, IsT.W. of St. David's) these are again overlaid by the " Arenig, 

 or Skiddaw group " and the Llandeilo flags. Each of the sections 

 has shown fossil traces after a long and persevering search. But 

 the section at Porth Ehaw is not only the typical one, but contains 

 all the principal fossil types — trilobites of six or seven genera, and 

 about fifteen species ; Brachiopod and Pteropod shells, Cystideas, 

 and sponges of two or three different kinds. All of them are 

 distinct as to species, and many as to genera also, from the over- 

 lying rocks of the true " Lingula Flags." 



The history of discovery in the Palseozoic rocks has hitherto 

 been that every group beneath the Old Eed Sandstone, containing 

 a distinct fauna, has, when its relative position and mineral structure 

 is ascertained, received a separate name. The authors hold it there- 

 fore of prime importance not to confound this fauna with that of 

 any of the overlying rocks of the Lower Silurian, or even of the 

 Upper Cambrian groups. If Llandeilo, Caradoc, Llandovery, and 

 Wenlock imply distinct periods of creation, much more does the 

 term "Lingula Flags" or "Ffestiniog group" indicate a distinct 



