250 PROCEEDINGS OF THE &EOLOQICAL SOCIETY. [Mar. 8, 



regard to other dolomites. That the Magnesian Limestone was de- 

 posited in great part from solutions may partly accotmt for the 

 absence of fossUs in so much of that formation ; and the uncon- 

 genial nature of the waters of a salt lake may account for the 

 poverty-stricken character of the whole molluscan fauna. 



One other group of red or purple strata remains, older than the 

 Old Eed Sandstone, and of this I speak with more doubt ; I mean 

 the Cambrian rocks. Neither in North Wales nor in the Longmynd 

 do these rocks afford any indications of life, excepting annelide- 

 tracks and burrows ; for, with some other persons, I consider that 

 the so-called trilobite Palceopyge Ramsay i is only an accidental 

 marking simulating the form of a trilobite*. The general absence 

 of Mollusca in these strata, and the sudden appearance of shells and 

 trilobites in quantity in the succeeding Lingula-S.a,ga, indicates a 

 sudden change of conditions. There is perfect conformity between 

 the two formations ; but the change of lithological character is rapid, 

 and akin to that which marks the change from Upper Silurian rocks 

 into Old Eed Sandstone ; only the order of change is reversed. 

 Beheving that the red colour of rocks is apt to be connected with 

 their deposition in inland waters, I conceive it to be possible that 

 the absence of marine Mollusca in the Cambrian rocks may be due 

 to the same cause that produced their absence in the Old Red Sand- 

 stone. The presence of sun-cracks and rain-pittings in the Longmynd 

 beds favours this suggestion. In Pembrokeshire, however, Mr. Hicks 

 has discovered a Lingulella {L. ferrugined) and Leperditia cambrensis 

 on two horizons, in strata well down in the purple Cambrian series. 

 It is, however, worthy of note that the lowest slaty bed in which the 

 fossil occurs, directly overlies " olive-green grits and shales" f. These 

 may possibly mark occasional influxes of the sea into inland waters, 

 due to oscillations of level. I do not wish, however, to speak positively 

 on these Pembrokeshire strata. It is nearly thirty years since I 

 mapped the country, and I should like again to see the rocks in 

 place before doing any thing more than merely hinting at the subject. 

 It is worthy of remark, however, that the possible inland origin of 

 the Cambrian deposits in general is quite consistent with and throws 

 some light on the statement by Dr. Otto Torell of the occurrence 

 of land-plants in these strata, supposing this statement to be 

 correct. 



If I am right in the deductions I have drawn in treating of the 

 red rocks and magnesian limestone of older date than the Trias, 

 some remarkable conclusions may be arrived at in connexion with 

 the inland character of the waters of the epochs to which this and 

 my previous paper on the New Ked Marl relate. 



The old palaeozoic area of Bristol and the Mendip Hills and of 

 adjacent districts nowpartly concealed by secondary strata stood above 

 water during the whole of the periods of deposition of the Permian 

 and Bunter beds, and was not covered with water till these were more 



* "The mythical PalcBopyge" (Salter, Quart. Journ. Geol. Soc. Tol. rxiii. 

 p. 340). 



t Q-eol. Mag. A'ol. T. p. 306, 



