Reports & Proceedings — Geological Society of London. 45 



a ratio of Mg to Fe of about 2. The iron and olivine are very 

 unevenly distribr.ted, and have chemical compositions such as they 

 have in the pallasites, the iron being poor in nickel (ratio of Fe to 

 Ni generally greater than 10), and the olivine poor in ferrous oxide 

 (ratio of Mg to Fe from 6 to 9). In accordance with the author's 

 conception of a genetic relationship of meteorites, it is suggested that 

 a eucrite-like magma, i.e. one of higher oxidation, was invaded by 

 a pallasite-like magma of lower oxidation. The curiously unequal 

 distribution of tlie nickel-iron and the shattered (cataclastic) 

 structure which, is generally confined to the parts rich in iron 

 support this view. 



Professor H. Hilton : On Changing the Plane of a Gnomonic or 

 Stereographic Projection. A method was described by means of 

 which the gnomonic or stereographic projection of a crystal on any 

 plane may be obtained when the projection on one plane is given. 

 The application to the drawing or orthographic projection of the 

 crystal was also discussed. 



Pi'ofessor H. Hilton: On Cleavage Angle in a llandom Section o-f 

 a crystal. A graphical method was given by means of which it is 

 possible to calculate the chance that the angle between the cleavage- 

 cracks on a random section of a crystal with two good cleavages may 

 lie between specified limits. The method was worked out in detail 

 for the cases in which the angle between the cleavage-planes was 

 90° or 60^. 



IV. — Geological Society of London. 



JSTovemher 21, 1917.— Dr. Alfred Harker, F.R.S., President, in the 



Chair. 

 The following communication was read : — 



" The Shap Minor Intrusions." By James Morrison, B.A., B.Sc. 

 (Communicated by Dr. Herbert Lapworth, Sec. G.S., M.Inst. C.E.) 



The paper deals with the minor igneous intrusions occurring in 

 the triangular area between Shap, Windermere, and Sedbergh. 



From their field relations and petrographic characters the in- 

 trusions are fonnd to belong to one or the other of two well-marked 

 groups, a division which is regarded as connoting also an age- 

 classification. 



The rocks of the earlier set, characterized by the presence of large 

 orthoclase-felspars of the granitic type, are intimately associated 

 with the granite, to the immediate neighbourhood of which they are 

 practically confined. The rocks range from quartz-felsites to lampro- 

 phyres. Of considerable interest in this group is a series of hybrid 

 intrusions, consisting essentially of rocks of a more or less basic 

 magma enclosing xenocrysts of a more acid (but allied) magma 

 obtained by settlement under intratelluric conditions. The constitu- 

 tion of any given member of the series is determined by two factors : 

 the abundance of xenocrysts and the composition of the matrix, an 

 increasing basicity in the latter (due to original magmatic differentia- 

 tion) and a decrease in the former marking the successive stages. 

 The more acid have affinities with the porphyrites, the more basic 



