20 GEOLOGY. 



Cambrian series (Menevian, Middle Arenig, and Tromadoc) are toler- 

 ably rich in phosphate of lime, amounting to 10 p. c. in some cases. 

 Those parts which contain much phosphate are also those which contain 

 most Crustacea. The shells of Crustacea are always rich in phosphate 

 of lime ; those of the Trilobites seem to have been so likewise. The 

 shell of Paradoxldes contains from 40 to 50 p. c. of phosphate of lime. 

 Beds which contain few Trilobites are poor in phosphate. From these 

 facts the author infers that the phosphate of the Cambrian rocks was 

 mainly produced by the Crustacea. The phosphatic rocks are some- 

 times traversed by trap dykes ; it is then found that the phosphate has 

 been removed from the rock and has become concentrated in the trap, 

 especially near the edges of the dykes. Mr. Hudleston gives details of 

 analyses of the rocks and of recent lobsters. The amount of phosphate 

 in the Trilobite shell is much in excess of that in recent Crustacea ; he 

 infers that the excess is due to substitution. He discusses the removal 

 of phosphate from the rock by trap dykes, and suggests that the phos- 

 phate may formerly have been more abundant in the dykes than now, 

 as the trap is in an altered state. W. T. 



Hicks, H. The Physical Conditions under which the Cambrian and 

 Lower Silurian Eocks were probably deposited over the European 

 Area. Quart. Journ. Geol. Soc. vol. xxxi. pp. 552-558, plate. 



A pre-Cambrian continent extended over the area now occupied by 

 Europe ; the land was highest to the N.E., lowest to the S.W". During 

 the Cambrian period (Longmynd to Tremadoc) this continent slowly 

 sank ; but dry land probably existed to the beginning of the Devonian 

 period in the E. part. The S.W. part of this old continent was first 

 submerged ; but how far S.W. the continent extended is not known. 

 The earliest deposits known are those in the British Isles and Spain ; 

 and here the series is most complete. As the land sank the sea spread 

 further east, the earliest deposits in this direction being later in time 

 than those of the west. The order of events is given in detail for the 

 Welsh area. At the close of the L. Silurian period the sea-bottom was 

 possibly raised above water in some places ; this elevation seems to have 

 occurred chiefly along the line of volcanic action. The author traces 

 out the migration of the fauna, with reference to the theory of evolu- 

 tion. The earliest faunas were of lower forms than the later : this 

 difference is most marked in the western areas ; and here we find the 

 greater number of genera, and the genera here show a greater number 

 of stages of progression than they do in the eastern areas. The inter- 

 mediate varieties did not reach so far east, just as other intermediate 

 forms did not reach the European area at all. Only the stronger and 

 more marked varieties, which we now know as species, were able to 

 pass on. W. T. 



Holt, James. The Millstone Grit, or that Stratification of Rock 

 chiefly found in the Neighbourhood of Bolton. Papers Land and 

 Water Club, Bolton, f^ess. 1873-4 and 1874-5, pp. 54-59. 



A popular account of the Millstone Grit. 



