REVIEWS. 413 



extreme sensitiveness of quartz to pressure is emphasized (as it has been 

 by Lehmann and the present writer) and illustrated by undulatory 

 extinction, banding, granulation and even plastic bending around other 

 minerals. Dynamic action is regarded as the efificient cause of the 

 secondary impregnation of feldspar by quartz, and a union of this with 

 weathering of the feldspar as the source of the abundant and complex 

 pegmatitic intergrowths of quartz and feldspar. 



These results are important, and they will now doubtless come to 

 be generally recognized. It is, however, of interest to observe in this 

 connection that all which is here announced as new in regard to sec- 

 ondary and " corrosion " quartz was described and figured in even 

 greater detail by Prof. R. D. Irving ten years ago. This does not 

 appear to be known to Dr, Romberg, for he does not allude to it, but 

 anvone who will turn to pages 99 to 124 and plates XIII, XIV and XV 

 of the monograph on the Lake Superior Copper Rocks (vol. 5, U. S. 

 Geol. Survey, Washington, 1883) will find his conclusions stated in 

 almost the same language and with a much wider range of fact and illus- 

 tration. Dynamic action is not here adduced as a cause for the satura- 

 tion of feldspar by secondary micropegraatitic quartz, since the Lake 

 Superior rocks show no evidence of having been subjected to pressure, 

 but that the quartz itself has been derived from the leaching of the 

 feldspar substance and that the impregnation is mostly confined to the 

 orthoclase is clearly stated. 



Dr. Romberg also demonstrates, in a number of cases, the second- 

 ary origin of albite, especially as microperthite, and of microline. He 

 gives details relating to each of the mineral constituents, and then the 

 effects of pressure and of chemical action on the most important of 

 them. Among many interesting observations but a few can be even 

 mentioned here; such, for instance, as the original character of musco- 

 vite in many granites ; the alteration of garnet into muscovite ; the 

 dependence of the well - known pleochroichalos in biotite and cordier- 

 ite upon the substance of the zircon which they almost invariably sur- 

 round, and secondary rutile needles which grow out from biotite into 

 both quartz and feldspar. In one rock occurring in a granite a violet, 

 strongly pleochroic mineral was found, which, in neither composition 

 nor physical properties, agreed exactly with any known species. It 

 seems to be intermediate between andalusite and dumortierite, but, as 

 its individuality is not yet perfectly established, no new name is pro- 

 posed for it. G. H. Williams. 



