THE CAMBRIAN SYSTEM 99 



of green igneous rock. Dr. Peach reports that the fossils include 

 species of Lingulella, Obolella, Acrotreta, Linnarstonia, and Siphono- 

 treta, and a few specimens of a Phyllocarid Crustacean allied to 

 Lingulocaris. These genera, he remarks, are found in both Upper 

 Cambrian and Lower Ordovician, but the absence of graptolites is 

 indicative of the former rather than the latter. 



D. THE CAMBRIAN OP NORTHERN EUROPE 

 1. France (North-WegV) 



Cambrian strata are found in many parts of Brittany and 

 Normandy troughed in between the tracts of Archa;an rocks, the 

 main flexures of the distriet striking roughly from west to east 

 The system is most fully developed in the southern and eastern 

 parts of the region, some portions of it being apparently absent in 

 the west and north. 



In the north-west (around Brest and Trdguier) the Cambrian 

 Series consists of two groups differing much in lithological 

 characters. These are (1) a basal purple conglomerate passing 

 up into sandstones, 300 to 500 feet, (2) purple and green slates, 

 about 400 feet. 24 No fossils have been found in these rocks, and 

 they are succeeded by coarse grey felspathic sandstones (Grit 

 . felspathique), which are either of Tremadoc or Arenig age. 



In the south and south-east of Brittany the Cambrian is repre- 

 sented by much thicker masses of deposit. Thus to the south and 

 weet of Rennes the purple conglomerate and sandstone is 1700 

 feet thick, and the overlying slates are estimated to be 7000 feet 

 Farther east in Mayenne there is a more varied series comprising 

 a basal conglomerate, purple slates with beds of grit and limestone, 

 coarse sandstones, and andesitic lavas, \\ith finally green slates 

 containing Lingulella Criei. In the lower beds only a few 

 specimens of Lingulella and Dinobolus have yet been found, but 

 Mr. ^Ehlert believes them to represent the whole of the Lower and 

 Middle Cambrian Series (Olenellian and Paradoxidian). 25 



The correlation of the southern and northern series is not eay 

 because of the rarity of fossils. Professor de Lapparent gave no 

 definite correlation, but seemed to assume that the basal con- 

 glomerates are everywhere of the same age. If this is so then 

 there is probably a gap in the northern series between the 

 slates and the Grh felspathique. On the other hand, t he- 

 northern area may have been land in Lower Cambrian time, 

 and the conglomerates may be shore deposits which would be 

 of later and later date as we passed from south to north and 



