354 L. Richardson — 



bostonites is soda-orthoclase. With the incoming of lime, as in, 

 maenaites, the latter is replaced chiefly by oligoclase. 



Although a perfect flow-structure was a striking feature of the 

 original bostonites, it is doubtful whether this name can with 

 advantage be restricted to rocks showing this texture. Rocks 

 undoubtedly exist which chemically, miueralogically, and 

 genetically are like the type bostonites, bat which differ from them 

 in texture. Are these to be given ncAV nam.es, or are they not 

 sufficiently described l-y using " bostonite ", with an appropriate 

 textural qualifier ? It must be admitted that the presence or 

 absence of flow structure is of no petrogenetic significance, and 

 therefore of no classificatory value. The writer would much prefer 

 to use the name for a rock containing a certain assemblage of 

 minerals, and derived always from the same parent magma. 

 Bostonite is known to be one of the ultimate products of 

 differentiation of a soda-syenitic magma, those derived from nord- 

 markite carrying free quartz, those derived from laurvikite being 

 free from this mmeral. Now a true bostonite can be born of no other 

 parents, neither calc-alkaline nor spilitic. For example, it is a 

 mistaken policy to designate as " bostonite " acid veins in an albite- 

 diabase from East Devonshire.^ The latter rock is a spilitic rock, 

 probably the intrusive representative of the spilites. The straining 

 of this magma towards the alkali pole would result in the production 

 of a keratophyric not of a bostonitic rook. 



The essential difference between keratophyre and bostonite lies 

 not so much in mineral composition and texture, as in descent. 

 By taking descent duly into account all danger of overlapping 

 disappears, even with rocks wldch may be so nearly homeomorphic 

 as these two sometmics are. 



A Boring at Calcutt, near Cricklade, Wiltshire. 



By L. Richardson. 



IN the early half of 1922 a boring ("jumped") was made by 

 Mr. H. G. Godwin, of Quenington, Fairford, Gloucestershire, for 

 Mr. Oswald Collier, of Calcutt, in search of water. The site of the 

 borehole is at Calcutt — \m. above the "C" in Calcutt on 6 in. 

 map, 5 S.W., Wilts. 



Calcutt is on the Oxford Clay, 3i miles south-east of the outcrop 

 of the basement-beds of the formation near The Fosse (by the side of 

 the Ermin Street, about half-way between Cricklade and Cirencester), 

 and 2| miles north-west of the outcrop of the top-beds of the 

 formation near Broad Blunsdon, where the Oxford Clay is succeeded 

 by the Corallian. 



1 Abstracts from Proc. Geol. Soc. London, No. 1,076, 1921, p. ii. 



