266 Day and Shepherd — Lime-Silica Series of Minerals. 



mineral and rock formation can now be competently studied. 

 The question is now, rather, how much of it all can we actually 

 carry out? Vogt has already shown us,* in a paper published 

 only a few months ago, that a great deal can be accomplished 

 by a judicious treatment of existing observations, particularly 

 the more trustworthy of the mineral and rock analyses, when 

 combined with extensive field experience. 



It has been the purpose of this laboratory to attempt this 

 task by a direct application of the principles and methods of 

 quantitative physics and chemistry, or, in a word, to study 

 mineral and rock formation by direct measurement at the tem- 

 peratures where the minerals combine and separate like the 

 solutions of ordinary chemistry under ordinary conditions. 

 We further determined, wherever possible, to prepare chemi- 

 cally pure minerals for this purpose in order that such conclu- 

 sions as we might reach should not be dependent upon danger- 

 ous assumptions regarding the harmless character of the five 

 or ten per cent of " impurities " not infrequently present in 

 hand specimens from natural sources. It is at once obvious 

 that in order to succeed, the first experiments must be restricted 

 to the simplest reactions, and that these will not always be the 

 most important or the most interesting, but the results will 

 always be in definite terms and final when the materials used 

 are pure. Furthermore, the accumulated experience obtained 

 from simple cases will safely and surely lead to successful 

 methods of a scope to meet the more complicated problems of 

 rock formation. 



This plan was really entered upon several years ago in a 

 small way and with very limited resources. The first paper, 

 which was published in 1904-05, contained a laboratory 

 study of a typical isomorphous pair, the soda-lime feldspar 

 series, carried out in the spirit of the above plan. The second, 

 which appeared in February of the present year, was a very 

 careful study of enantiotropic mineral inversion between the 

 mineral wollastonite and the pseudo-hexagonal form which has 

 been obtained by several observers but which appears not to 

 have been found in nature. The present paper, which is the 

 third of the mineralogical series, undertakes to carry through 

 a fairly complete set of measurements upon a typical eutectic 

 pair — the lime-silica series. It is still incomplete in some 

 particulars, notably at the ends of the series. Mixtures very 

 rich in lime possess temperature constants which are beyond 

 the reach of existing apparatus, while on the silica side the 

 extreme viscosity and consequent inertness which were encoun- 

 tered in the soda feldspars, effectually veil or prevent the 

 development of the phenomena which occur there. Some 

 approximate measurements have been made even in these 



* J. H. L. Vogt, Physikalisch-Chemische Gesetze der Krystallisations- 

 foJge in Eraptivgesteinen, Tschermak Min. u. petr. Mitth., xxiv, 437, 1906. 



