n^OTiES j^jsriD Q,T7:EI^I:E]s. 



1.— True Syenite is an aggregate of Amphibole and Ortlioclase, and quartz is often 

 present (this ignores all other accessories present). If a rock consists of Amphibole 

 +Orthoclase+Uligoclase, what should it be called ? Quartz may be also present, 

 not necessarily an essential — G. H. K. (Answer to 1. " Syenite '' still. — T. R. J.) 



2. — Kaolin occurs as a decomposed Felstone in situ. Does it often occur as a 

 subaqueous rock, and where >—G. H. K. (Answer to 2. " As the white pipe-clay 

 of Bovey-Tracey, Wareham, Bournemouth, Alum Bay," etc. T. R. J.) 



3. — In speaking of the typical varieties of the felspars, Orthoclase, Oligoclase, and 

 Labradorite, we wish to express the proportions of acid in each case. How can we 

 do this .f Is not Orthoclase a neutral or fully saturated salt. What prefix can be 

 applied to the felspar in order to express the proportion of the saturation in each 

 case, — H. L. 



4. — Dana gives as Diorite a compound of Amphibole and Albite. This, however, 

 appears to be incorrect, as Diorite ought to be a compound of Amphibole and Ortho- 

 clase, with or without Labradorite. What is the proper name for a compound of 

 Amphibole and Albite, and when does it occur ? — G. H. K. 



5. — Daubuisson gave the name of Eurite to certain felstones on account of their 

 fusibility, in fact to basic felstones in which Orthoclase was not present, or only in 

 a subordinate quantity. Some authorities confine the name to an almost compact 

 rock, an intimate mixture of Felspar and Quartz, occasionally showing specks of quartz. 

 Still, however, there are more or less granular rocks, which must be classed among 

 the Enrites, as they merge the one into the other. In some of these granular rocks 

 Amphibole is visible, and by some the rock would be called Diorite. What per- 

 centage of Amphibole ought a Diorite to contain } (By a Diorite I mean a rock 

 principally composed of Amphibole and Felspar, not Orthoclase.) — H. L. 



6 — Naumann confines the term Greenstone to Diabase, Brongniart to Diorite. Jukes, 

 Cotta, and others use it, as a general rule, for all basic Plutonic rocks (the Trappean 

 rocks of Jukes). To which class of rock is it best to apply it ? — H. L. (Answer to 

 6. " Use ' Greenstone ' as a general term for greenish trap-rocks ; and do not make 

 a special term of it." T. E. J.) 



7— Lyell, in his new work (The Student's Elements of Geology), mentions that " the 

 recent researches of Vom Rath and others, prove that the Mineral Tridymite, which 

 is crystallized Silica of sp. gr. 2-3, is of common occurrence in the Volcanic Eocks of 

 Mexico, Auvergne, the Ehine, and elsewhere, although hitherto entirely overlooked." 

 Does it (Tridymite) occur as a rock constituent in these localities or as an accessory ? 

 In Trachyte, for instance, does it replace the ordinary quartz it may contain, is it as- 

 sociated with it, or does it merely occur in drusy cavities, and must its specific gravity 

 be ascertained, that its presence may be determined .^ — H. L. 



8.— Concretionary structure in a piece of plaster on the inside walls of a ruined 

 house on the banks of the Eniff river. Mayo, Ireland. To what is it due .!> Each 

 line seems to be an aggregate of minute crystals. The lines A and B seem to be 

 shrinkage fissures or joints.— G. H. K. (What is the plaster composed oU Edit.— 

 Geol. Mag.) 



A 



Concretionary Structure seen in old plastered wall, Co. Mayo, Ireland. 



For Eock nomenclature " Cotta's Classification of Eocks" should be followed, we 

 have no other work at present which can be equally recommended to students. 

 Answers to rest of queries will appear nest month. — Edit. Geol, Mag. 



