Br. H. Hicks — Life Zones in Palceozoic Rocks. 447 



Lingula Flags and the Lower Tremarloc." In the year 1882 '■ 

 Professor Lapworth gave an account of the discovery by him in the 

 " Stockingford shales," near Birmingham, of " many of the most 

 typical Upper Cambrian Brachiopoda and Trilobites," a list of 

 M^hich he gives as follows : Acrotreta socialis, Obolella Salteri, 

 Lingulella ferruginea, Kutorgina cingulata, Agnostus pisiformis, 

 Lingulella NichoJsovi. 



In a paper in 1885 ^ by Mr. J. E. Marr and Mr. T. Eoberts is 

 given an account of the discovery by them of fossils characteristic of 

 the " Lingula Flags " in some " black iron-stained slates " which 

 are "well seen near Leweston, Trefgarn Bridge, and Spittal Cross, 

 in North Pembrokeshire. The species mentioned are Agnostus 

 pisiformis, var. socialis, and Olenus spinidosus. 



The "Tremadoc Slates" of Sedgwick were divided by Mr. Salter, 

 in 1857, into a Lower and Upper series. The fauna was stated by 

 him to be essentially Middle Cambrian (now Upper Cambrian), but 

 showing a tendency to include some few types characteristic of 

 higher horizons. " The species, however, ai'e all distinct, even from 

 those of the Arenig Group, and those of the Upper are distinct from 

 those of the Lower Tremadoc." ^ In the report by Mr. Salter and 

 myself to the British Association in 1866, we announced the dis- 

 covery of Tremadoc beds, " or what we regard as such," near St. 

 David's, for " lying as they do upon the true Lingula Flags, and 

 under the Arenig or Skiddaw Slates, they can hardly be anything 

 but Tremadoc beds." A list is given of the fossils which had then 

 been discovered by us, but many additional forms were sub- 

 sequently added to it. These were discovered during our continued 

 researches, carried on with occasional very valuable assistance from 

 Messrs. Homfray, Lightbody, Hopkinson, and Kershaw. The 

 fossils, comprising a rich and exceedingly interesting fauna (in 

 which the earliest lamellibranchs, encrinites, and star-fish up to 

 that time discovered in Britain occurred), were described by me 

 in the Quarterly Journal of the Geological Society for February 

 1873, and at page 42 I stated that "the palceontological evidence 

 goes to prove that they (the Tremadoc rocks) are closely allied to, 

 if not identical with, the lower portion of the Tremadoc rocks of 

 North Wales," and that the " conditions under which these rocks at 

 St. David's were deposited seem to have been intermediate between 

 those of the shoal and shallow water of the Lingula Flag period 

 and those of the deep sea which must have prevailed when the fine 

 muddy deposits of the overlying Arenig slates were being thrown 

 down. This intermediate condition must have been particularly 

 favourable to the existence of life, and was doubtless one of the 

 causes of the appearance at this time of such a varied and important 

 group of organisms." 



The boundary-line between the Tremadoc rocks at St. David's 



1 Geol. Mag. Dec. II. Vol. IX. p. 565. 

 ^ Quart. Journ. Geol. Soc. vol. xli. p. 476. 



^ " Catalogue of the Collection of Cambrian and Silurian Fossils contained in the 

 Geological Museum of the University of Cambridge," 1873, p. 15. 



