PETROLOGICAL ABSTRACTS AND REVIEWS 277 



peratures below their inversion points. Either mineral will retain its 

 form when the temperature is reduced. Quartz, however, is probably 

 never deposited at temperatures greater than 870°. The inversion 

 point of quartz to tridymite is 870°+ 10°, and tridymite to cristo- 

 balite 1470°+ 10°. The a-^ inversion point of quartz at 575° is not 

 questioned. 



A. J. 



Flett, J. S., and Hill, J. B. The Geology of the Lizard and Meneage, 

 Mem. Geol. Survey England and Wales, Explanation of Sheet 

 359. London, 1912. Pp. 280, pi. 15, figs. 10. 



The rocks described are serpentines, peridotites, gabbros, dolerites, 

 epidiorites, gneisses, granite gneisses, greenstones, soda granite por- 

 phyries, granites, and schists, as well as sedimentary rocks. Many 

 analyses are given, and there are 24 fine heliotypes of rock sections. 



A. J. 



FooTE, W. M. "Preliminary Note on the Shower of Meteoric 

 Stones at Aztec, near Holbrook, Navajo County, Arizona," 

 Amer. Jour. Sci., XXXIV (1912), 437-56, figs. 17. 

 In the meteoric fall at Holbrook, Ariz., July 19, 191 2, over 14,000 

 stones are recorded, with a total weight of 218,310 grams. 



^^___ A. J. 



Galpin, Sydney Longman. "Studies of Flint Clays and Their 

 Associates," Trans. Amer. Ceramic Soc., XIV (191 2), 301-46. 

 From geologic occurrences, dehydration tests, and microscopic ex- 

 amination, the author concludes: (i) Flint clays have been formed by 

 the setting and recrystallization of fine-grained, largely colloidal sedi- 

 ments. The products of recrystallization are mainly kaolinite, with 

 minor amounts of hydrated micas. (2) The semi-flint or soft clays have 

 been derived from the flint clays through metamorphism, resulting in a 

 conversion of much kaolinite into hydro-micas. (3) Plastic fire clays 

 have resulted from long weathering of the soft clays. They contain a 

 high percentage of hydro-mica. (4) The change from muscovite 

 through hydrated or hydro-micas to kaolinite may take place without 

 destruction of the original structure, indicating the possibility of an 

 isomorphous series embracing all of these minerals. 



A.J. 



