362 The Rev. Prof. Blake — Base of the Sedimentary Series. 



off from the overlying Cambrian ; the Bangor beds are not marked 

 off by any great interval. But on both these points there are differ- 

 ences of opinion. Pending therefore further evidence, one " view " 

 is as good as another. My own at present tends rather to give 

 more weight to the Bangor succession than to the St. Davids, and 

 to classify the Uriconians, if they must be classified, with the over- 

 lying though unconformable Cambrians. There remain the gneisses 

 and massive igneous rocks of the Wrekin and the Rushton schists. 

 But here again we have nothing but "view." Both are certainly 

 older than the Cambrian quartzite, but are they older than the 

 Uriconians ? As to the Rushton schists, there is no positive evidence 

 whatever. They are most like some rocks in Anglesey of any I 

 know, and I therefore think they are older even than the Longmynd, 

 a fortiori than the Uriconian. In the Wrekin itself there is too 

 much faulting at the junction of the eurite with the rhyolites for 

 any positive evidence to be produced ; but I think the former is 

 intrusive in the latter, because of its mode of occurrence, and 

 because other small patches like it are found isolated in the 

 rhyolites like intrusive bosses. At Charlton Hill, Dr. Callaway, as 

 before noted, has found conglomerates which, if they were part of 

 the Uriconian, would prove these to be the younger by containing 

 eurite pebbles ; but according to my observations these conglo- 

 merates are merely superficial, and probably belong to the lowest 

 Cambrian, so that evidence fails us. As to the gneiss of Primrose 

 Hill, it is such a tiny patch, and is associated with another tiny 

 patch of hornblende schist, that it seems impossible to have been 

 formed on the spot; and my "view" accordingly is that these 

 patches are masses of lower rock brought up in the eruption of the 

 eurite. All I feel sure of, however, is that the contrary supposition 

 is no more than a " view." 



6. Devonshire and Cornwall. — In this area we have mica and 

 hornblende schists which are considered by Prof. Bonney and Gen. 

 McMahon to be Precambrian stratified rocks. By Mr. Teall and 

 others they are thought to be dynamically metamorphosed igneous 

 rocks. I do not know the district at all, though I hope to study it 

 shortly. If, however, as Prof. Bonney says, some of the rocks bear 

 a striking resemblance to the chloritic schists of Holyhead, this 

 would be a justification of the view that they are really Lower 

 Monian, if it were safe to judge by mineralogical similarity alone. 



Such is the present state of the knowledge acquired on Precam- 

 brian rocks in England and Wales. Probably few of the conclusions 

 above stated are universally accepted, which is not perhaps to be 

 wondered at, as no conclusions could possibly be stated that are. 



What I have here given have been arrived at by making further 

 observations to test the hypotheses which have been suggested to 

 others by a smaller number of facts. Where these further obser- 

 vations have led to different conclusions, the latter can only be 

 legitimately overthrown, by proving that these observations are 

 wrong, or by making still further ones in the several districts. It 

 will be only a waste of time to reiterate old statements which have 

 been thus tested and found wanting. 



