1870.] Relation between Sun's Altitude and Chemical Intensity. 301 



still in the Cainozoic or Cretaceous age would hardly be consistent with the 

 necessary terminology of geological science. 



During the end of the Miocene age and the whole of the Pliocene the 

 Sicilian area was occupied by a deep sea. The distinction between the 

 faunas of those times and the present becomes less, year after year, as 

 science progresses ; and it is evident that a great number of existing species 

 of nearly every class flourished before the occurrence of the great changes 

 in physical geology which have become the artificial breaks of tertiary 

 geologists. That the Cainozoic deep-sea corals should resemble, and in 

 some instances should be identical in species with, the forms now inhabiting 

 vast depths, is therefore quite in accordance with the philosophy of modern 

 geology. Before the deposition of the Cainozoic strata, and whilst the 

 deep-sea deposits of the Eocene age were collecting in the Franco-British 

 area, there was a Madreporarian fauna there which was singularly like unto 

 that which followed it, both as regards the shape of the forms and their 

 genera. Still earlier, during the slow subsidence of the great Upper Cre- 

 taceous deep-sea area, there was a coral-fauna in the north and west of 

 Europe, of which the existing is very representative. The simple forms 

 predominate in both faunas. Caryophyllia is a dominant genus in either ; 

 and a branching Synhelia of the old fauna is replaced in the present state 

 of things by a branching Lophohelia. The similarity of deep-sea coral- 

 faunas might be carried still further back in the world's history ; but it 

 must be enough for my purpose to assert the representative character and the 

 homotaxis of the Upper Cretaceous, the Tertiary, and the existing deep- 

 sea coral-faunas. This character is enhanced by the persistence of types ; 

 but still the representative faunas are separable by vast intervals of time. 



March 31, 1870. 



Lieut.-General Sir EDWARD SABINE, K.C.B., President, in 



the Chair. 



The following communications were read : — 



I. " On the Relation between the Sun's Altitude and the Chemical 

 Intensity of Total Daylight in a Cloudless Sky." By Henry 

 E. Roscoe, F.R.S., and T. E. Thorpe, Ph.D. Received March 

 3, 1870. 



(Abstract.) 



In this communication the authors give the results of a series of deter- 

 minations of the chemical intensity of total daylight made in the autumn 

 of 1867 on the flat tableland on the southern side of the Tagus, about 

 8£ miles to the south-east of Lisbon, under a cloudless sky, with the object 

 of ascertaining the relation existing between the solar altitude and the 



