RECENT ADVANCES IN SCIENCE 453 



Cambrian beds. These facts also confirm the widely accepted 

 opinion of the Pre-Cambrian age of the " Mona complex " of 

 Anglesey. There is a great unconformity at the base of the 

 Arenig in this area, which supports Ramsay's original views 

 as to the relation of the Arenig to the subjacent strata. 



Glaciology. — A shelly clay, containing erratics solely of 

 Scandinavian origin and with a fauna of Arctic affinities, has 

 been discovered on the Durham coast by Mr. C. T. Trechmann 

 {Quart. Jour. Geol. Soc. 1915, 71, 53). This drift underlies the 

 main Cheviot drift and appears to fill up hollows and fissures 

 in the Pre-Glacial land surface. It records perhaps the earliest 

 ice invasion of the English coast. In the discussion of the 

 paper Mr. G. W. Lamplugh supported the correlation of this 

 clay with the shelly Basement Boulder Clay of Yorkshire. 



The complicated history of the moraines of the great ice- 

 sheet in Indiana and Michigan, and the equally complicated 

 and interrelated glacial history of the Great Lakes is the subject 

 of an exhaustive work by F. Leverett and F. B. Taylor {United 

 States Geological Survey, Monograph 53, 1915). 



Petrology- Igneous Rocks. — A much-needed systematisation 

 of the microscopical characters of volcanic tuffs is provided by 

 Prof. L. V. Pirsson {Amer. Jour. Set. 191 5, 40, 191). He dis- 

 tinguishes between vitric tuffs, crystal tuffs, and lithic tuffs, 

 terms which explain themselves ; but is careful to point out 

 that there are all gradations between these groups. The 

 weathering, consolidation, devitrification, and metamorphism 

 of tuffs are also dealt with at length. 



An important study of the crystallisation of the ternary 

 system albite-anorthite-diopside has been carried out by N. L. 

 Bowen from a petrological point of view {Amer. Jour. Sci. 

 191 5, 40, 161). These mixtures may be regarded as simple 

 dioritic and basaltic magmas (haplodioritic, haplobasaltic). 

 It is shown that there are no diorite or gabbro eutectics, and 

 that the differentiation of such rocks is controlled entirely by 

 crystallisation. 



An exhaustive study of Hawaiian lavas, supported by 

 numerous first-rate chemical analyses, has been made by Whit- 

 man Cross {United States Geological Survey, 191 5, Professional 

 Paper, No. 88). While man}' of the rocks are ordinary plagio- 

 clase-basalts, a decided alkaline cast is given to the assemblage 

 by the presence of soda-trachytes, trachydolerites, with melilite- 



