400 Dr. H. Hicks — Life Zones in Paleozoic Rocks. 



research, by one of the authors of this paper. The search has been 

 systematically pursued since 1862, when the first fossil of the 

 Menevian Group was described by Mr. Salter from this neighbour- 

 hood ; and the labour has chiefly fallen upon Mr. Hicks, who resides 

 at St. David's. He has, literally, not left a stone unturned to find 

 the true place of OldJiamia, and, if possible, of the mythical Palceopyge 

 in these old red rocks. He has been rewarded, during the search, 

 by many additions to the Menevian fossils, found at successively 

 lower and lower horizons in the grey rocks which form the passage 

 from the Lower to the Upper Cambrians. But, until quite lately, 

 not a vestige had occurred to him in the actual red rocks them- 

 selves." I give these quotations as they clearly state what was 

 then known in regard to the evidences of life in the so-called 

 unaltered Cambrians as marked then and now on the Geological 

 Survey Maps. The boundary line it appears was first adopted by 

 Sir A. Eamsay when mapping the rocks in Pembrokeshire ; for in 

 the Geological Survey Memoirs, vol. iii., he says : " In 1841 the 

 Geological Survey began, to map the Silurian rocks at Haverfordwest, 

 in Pembrokeshire, and Sir Henry de la Beche was unable in that 

 neighbourhood to detect any base for the Silurian strata. In the 

 same year, at St. David's, I traced a provisional line between the 

 black and the purple slates, and this was afterwards adopted as 

 the line between the Silurian and Cambrian strata." It was well 

 known that the Cambrian as so defined contained in Pembrokeshire 

 a great thickness of strata, with somewhat marked lithological 

 characters ; therefore it was but natural when the equivalent rocks 

 in Merionethshire and Carnarvonshire were mapped in 1846 and 

 1848 that the Surveyors adopted the same name for these deposits, 

 as " strati graphically they occupy the same position, and litho- 

 logically they resemble each other." ^ 



After the Lingulella was found by me in the red rocks, in 1867, 

 I determined to search the underlying rocks systematically, and 

 with much care, in the hope of finding still lower zones of fossils ; 

 and in the following year, 1868, I was able to announce at the 

 meeting of the British Association that I had discovered several 

 zones of fossils in the Cambrian, the lowest being 1200 feet below 

 the red beds in which the previously described Lingulella had been 

 found. The fossils, it was stated, occur usually at intervals in the 

 strata ; " scores, and sometimes hundreds, of feet of strata apparently 

 intervening " between each zone. It was on this occasion also 

 that I proposed that the " Menevian Group " should henceforth be 

 included in Prof. Sedgwick's "Lower Cambrian" (the Cambrian 

 of the Survey), owing to the much greater likeness between the 

 fauna of the Menevian Group and the newly discovered fauna of 

 the underlying beds, than between that of the former and the over- 

 lying Lingula Flags. The fossils found in these beds were sub- 

 sequently described by me in the Quart. Journ. Geol. Soc. for 1871^; 



' Survey Memoirs, vol. iii. second edition, p. 8. 



2 "Descriptions of New Species of Fossils from the Longmynd Rocks of St. 

 David's." 



