October 28, 1920] 



NATURE 



283 



logical Survey, after a natural hesitation, had 

 frankly accepted and developed his conclusions ; 

 but many felt that to surrender large areas of 

 "altered Lower Silurian " on our maps to com- 

 batant claimants was a first step in the disintegra- 

 tion of the British Empire. On the other hand, 

 the word "mica-schist" was reserved by others 

 for a type of sediment that had not been repeated 

 since pre-cambrian times. Mr. Greenly came into 

 the field without any of these predilections, and 

 his memoir on Anglesey represents the reasoning 

 of an absolutely unhampered mind. 



His first volume is devoted to the "Mona com- 

 plex," which is regarded as probably pre-cambrian 



(p. 142). The details of folding and of foliation in 

 the successive divisions of the complex, and of 

 the spilitic lavas, with their associated red jaspers, 

 are finely illustrated in the author's plates. Two 

 of his broader landscapes have been selected for 

 the present notice. The word "encarsioblast " is 

 introduced on p. 43 for a lenticular crystalline 

 growth in a schist, in which the cleavages and 

 planes of intergrowth are at a high angle to the 

 general foliation, features indicating that such 

 growths are among the latest features of recon- 

 struction. When a term like this is written in 

 international Greek, cannot we get rid of "horn- 

 fels " and "augen" from British usage? The 



-Topical KcfMry of the Mona complex; Amlwch Port Mour. From "The Geology of Anglesey," by parmiuiou of Hts Majesty's 



SlalioMfy Oflke. 



throughout. The green rocks, including the 

 pillow-lavas of Newborough, are included in one 

 of the earliest divisions — the Gwna "group." 

 With J. F. Blake the author recognises (p. 896) 

 this "group " in Howth, in eastern Ireland — a 

 view that carries with it far wider suggestions. 

 Gneisses underlie the Mona complex, but an un- 

 conformity has not been traced ; the typical gneiss 

 (P- '3.1) '■'' composite, consisting of a granitoid 

 element veining and permeating an originally 

 sedimentary scries, which includes even lime- 

 stones. The resemblance with the gneiss of 

 eastern Suthcrlandshirc and Forfarshire is close 

 NO. 266t, VOL. 106] 



metamorphic rocks of Anglesey are admirably 

 dealt with, and the glaucophane-schists are held 

 (p. 120) to be modifications of the Gwna spilitic 

 lavas. 



The geological systems in Anglesey range up 

 to the Coal Measures, in which the barren red 

 strata of Malidracth and the Mcnai Strait are 

 now included (p. 668) ; but we must pass on to 

 the features impressed on the island by denuda- 

 tion and deposition since Cretaceous times. Mr. 

 Greenly (p. 777) shows the probability of a large 

 outlier of Chalk, resting on Jurassic beds, re- 

 m.Tining in the sen Ivtween the Isle of Man and 



