212 Scientific Intelligence. 



the structural parts of aeroplanes ; for very thin sheets to serve 

 as a strong and non-inflammable covering for aeroplane wings. 

 A considerable section of the report is devoted to gauge 

 testing by means of optical projectors. f. e. b. 



II. Geology and Mix paralogy. 



1. The Geology of Anglesey ; by Edward Greenly. Vols. 

 I and II, pp. 980, with 60 plates in the text, 17 folding plates, 

 and 346 text figures. Memoir of /the Geological Survey of Great 

 Britain, 1919. — These two handsome volumes, excellently illus- 

 trated and well bound, embody the results of the author's work 

 on the geology of Anglesey during a period of twenty-four years. 

 Greenly resigned from the Geological Survey in 1895, but, within 

 a few weeks after his resignation, he began a detailed study of 

 Anglesey, being irresistibly^ drawn to this task by the fascination 

 of the crystalline schists. In appreciative recognition of his 

 work the Geological Society of London has lately awarded him 

 the Lyell medal. 



Volume I deals with the Mona Complex, as the metamorphic 

 rocks of Anglesey are termed. They have long been of chief 

 interest in the geology of the island. They embrace an area of 

 200 square miles and are by far the largest area of metamorphic 

 rocks in southern Bi'itain. They are of Pre-Cambrian age and 

 are 20,000 feet thick, exclusive of the gneisses upon which the 

 other members of the Complex are supposed to lie unconform- 

 ably. The Mona Complex lends itself particularly well to a study 

 of the relation of the degree of metamorphism to the tectonics. 

 The author has been able to recognize three different successions 

 in the Complex : a stratigraphic, a tectonic, and a metamorphic. 

 The rocks have been folded into three master primary recumbent 

 folds, the horizontal amplitude of which is as much as 60 miles. 

 Superimposed on the primary folds are secondary and subordi- 

 nate folds, probably due to the same dynamic impulse that pro- 

 duced the major folding. The regional metamorphism of the 

 Mona Complex is of dynamic origin, and is ascribed to the super- 

 imposed foldings. The three primary recumbent folds, piled one 

 on the other, constitute three tectonic horizons, within each of 

 which the intensity of metamorphism progressively decreases 

 upward. Thus, a waxing and waning of metamorphism is 

 repeated thrice hypsometrically. The author explains this 

 remarkable sequence by the fact that although metamorphism is 

 a function of depth, it is a function of the thickness of the cover 

 that was present at the time it was developing, not of the cover 

 that may have been imposed after it had developed. Metamor- 

 phism may develop in a higher fold without appreciably intensi- 

 fying the crystalline condition of a subjacent fold. For the con- 

 version of the energy of folding into the molecular energy neces- 

 sary to effect metamorphism can take place only at the actual 

 locus of folding, and the underlying fold was therefore metamor- 

 phically inert, dead, when the next recumbent fold was rolled 

 over it. 



