Geology and Mineralogy . 185 



the igneous mass has been so deeply bitten into that only a rem- 

 nant remains, to those where only at the top is a small portion of 

 it revealed and finally the case where no igneous rock is seen but 

 must be inferred from the structure and associations of the 

 domed elevation. The igneous rocks composing these masses 

 present several varieties of feldspar porphyry, quite similar to 

 those found in the laccoliths of Colorado and Montana. 



This region was visited and briefly studied in the autumn of 

 1897 by those geologists who took part in the excursion to the 

 Caucasus of the Vllth International Congress at St. Petersburg 

 and it afforded to the European members of the party an excel- 

 lent and instructive example of geological phenomena which 

 many of them had until then regarded as confined to America, 

 and which hitherto they had not had an opportunity of seeing. 



The area has now been studied and mapped by the author 

 quoted above and the results of the work which have been car- 

 ried out under the direction of Prof. Duparc of Geneva, are given 

 in full, especially on the petrographic side. The rocks of the 

 different occurrences have been analyzed and in the conclusion a 

 number of deductions are drawn. This work will be of espe- 

 cial interest to many American geologists for its confirmation, 

 in another part of the world, of the results of their studies of the 

 phenomena of laccolithic intrusions. l. v. p. 



18. Physikalische Krystallographle und Ehdeitung in die 

 krystallographische Kenntnis der wichtigsten Substanzen / von 

 P. Groth. Pp. 820, with. 750 figures and 3 colored plates. 

 Leipzig, 1905 (Wilhelm Engelmann).— It is interesting to com- 

 pare the volume which has just appeared with its three predeces- 

 sors published at intervals during the past thirty years. The 

 increase in size from the 528 pages of the first edition (1876) to 

 the present volume, one-half larger, is the most apparent change, 

 but more important still is the development and expansion which 

 the successive works show in the principles and their applications 

 as they concern the topics embraced under Physical Crystallo- 

 graphy. The author has a happy power of assimilating and 

 making use of all that is most valuable and novel in the work of 

 others, and at the same time his own independent investigations 

 enable him not only to make important contributions of his own, 

 but also to bring the whole into a compact and homogeneous 

 system. The changes which the present edition exhibits most 

 particularly are those concerned with the classification and mutual 

 relations of the different physical properties. Something of this 

 will appear from the classification given in the Introduction. 



The physical characters of crystals are distinguished first as 

 scalar and vectorial. The former are those which are independent 

 of direction, as density, specific heat, etc., for crystals and all the 

 properties of amorphous substances. The latter embrace those 

 in which the direction is essential; further in regard. to them, 

 the term " bivectorial " is used for properties not acentric, that 

 is, similar in opposite directions from a given point. The bivec- 



Am. Jour. Sci. — Fourth Series, Vol. XXT, No. 122.— February, 1906. 

 13 



