336 Prof. A. C. Ramsay on Geological Ayes 



taining marine fossils are interstratified among the freshwater strata of 

 the Miocene rocks of Switzerland. The probability of these Cambrian 

 strata being partly of lacustrine origin is increased by the occurrence 

 of analogous beds beneath the Silurian strata of the Punjab. There, in 

 what is known as the Salt Range, I am informed by Professor Oldhain, 

 are certain red marly and sandy strata believed to be the general equi- 

 valents of our purple Cambrian rocks. They contain several thick beds 

 of rock-salt, such as could only have been deposited by supersaturation 

 due to solar evaporation, in the manner that rock-salt seems to have 

 been formed in the Keuper Marl. 



If the red Cambrian beds of Britain were partly deposited in inland 

 waters, then it appears likely that our Silurian formations, from the so- 

 called Menevian and Lingula beds upwards, were all deposited under 

 marine conditions between two continental epochs, the close of the 

 first of which is indicated by the nature of the Cambrian rocks, and the 

 beginning of the second by the passage of the Upper Ludlow beds into 

 the base of the Old Red Sandstone. 



The physical conditions and long duration of the second continental 

 epoch have been described in my two memoirs on the Red Rocks of Eng- 

 land *. The faunas of the Cambrian and Lingula-flag series (which pass 

 conformably into each other), in the comparative paucity of species and 

 their fragmentary character, seem partly to indicate occasional inland 

 shallow seas, possibly comparable to the great inlet of the Bay of Pundy ; 

 and this scanty life probably gives but a poor idea of the fuller fauna of 

 the period, hints of which we get from the equivalent formations of 

 Sweden and Bohemia. 



In the ' Geology of North "Wales ' (1866) I have shown that there is 

 a gradual passage between the Cambrian rocks and that portion of the 

 Lingula-flag series now sometimes called Menevian; and, for some years, 

 I have held that the whole series of formations, from the lowest known 

 Cambrian to the top of the Ludlow beds, may, in Britain, be most 

 conveniently classed under three groups : Cambrian, Lingula, and 

 Tremadoc slates form the lowest group, succeeded unconformably by 

 the second group, consisting of the Llandeilo and Bala, or Caradoc, 

 beds; above these we have the Llaiidovery, or May Hill, beds, over- 

 laidfrby the "Wenlock and Ludlow series, the Llandovery beds lying 

 quite unconformably on any and all of the formations of older date, from 

 the Cambrian to the Caradoc strata inclusive. "With each imconf onnable 

 break in stratigraphical succession there is a corresponding break in the 

 succession of species, very few (about 2\ per cent, out of 68 known 

 species) passing from the Tremadoc slate into the Llandeilo beds, while 



* Also in a lecture subsequently given at the Eoy.il Institution, in which this piece 

 of geological history was put into a more consecutive form, and the substance of 

 which Vas published in full in the 'Contemporary Review' for July 1873, and (in 

 Paris) in the 'Revue Scientifique' of 14th June. 



