552 H. HICKS ON THE DEPOSITION OF THE 



41. The Physical Conditions under which the Cambrian and Lower 

 Silurian Rocks were probably deposited over the European 

 Area. By Henry Hicks, Esq., E.G.S. (Head June 23, 1875.) 

 [Plate XXVII.] 



Wherever the base-line of the Cambrian rocks is seen throughout 

 the European area, it is found invariably to rest unconformably 

 upon an earlier series of rocks, which are supposed to be of the age 

 of the Laurentian rocks in Canada. These prse- Cambrian rocks in 

 Europe therefore, like the Laurentian rocks in America, indicate that 

 large continental areas existed previous to the deposition of the 

 Cambrian rocks. The European continent seems to have occupied 

 at that time a larger area than at present, and to have extended in 

 a continuous line from above Norway and Lapland to the south 

 coast of the Mediterranean, portions of this continent being now 

 apparently visible in Algiers and to the south of the Black Sea. In 

 an east-and-west line it would extend from at least the 100-fathom 

 line beyond the British Isles, to Asia. The higher land would be 

 towards the north-east; and the trend of the land would be in a 

 direction towards the south-west, a difference of level of probably 

 15,000 feet occurring between the higher lands to the east and the 

 low lands in the west. The surface of this continent seems to have 

 been more or less of an undulating character, with the higher ranges 

 running in the direction of east-north-east and west-south-west. 

 The strike of the immediately overlying beds usually takes this 

 course also ; and the now exposed portions of the old continent, 

 which then formed the higher points of the ranges, show also a long 

 axis in that direction. When therefore this continent began to 

 subside, the part facing the south-west became first covered over 

 by the sea ; and the direction in which the sea encroached is now 

 evident by a consideration of the order of the deposits as they were 

 thrown down, and of the successive faunas which became entombed. 

 We have no knowledge of how far the continent extended to the 

 south-west, nor of the thickness of deposits which may have taken 

 place over such areas if they existed; therefore for present pur- 

 poses we must consider the depression from the time only that 

 the record is preserved to us. The land which was lowest and 

 facing the Atlantic ocean, which doubtless then, as now, formed 

 one of the great oceanic basins, would become first submerged and 

 would receive deposits, whilst the higher portions would still remain 

 above water. The evidence derived from the consideration of the 

 deposits shows also that the depression of the prse-Cambrian land 

 was very gradual, and on the whole regular, and that the portions 

 the furthest to the north-east were the last to become submerged. 

 In England the Cambrian and Lower Silurian deposits attain to a 

 thickness of from 25,000 to 30,000 feet, exclusive of interbedded 

 tuff's or contemporaneous traps, whilst in Sweden the deposits repre- 

 sentative of these epochs do not attain to more than, at the most, 



