INVESTIGATIONS BY OTHERS. 



177 



poorness in augite. Moreover, the augite occurs only microscopically. The 

 European leucite rocks commonly bear thicker individuals of augite, and much 

 more of it, and also more magnetite, so that their color is a great deal darker. 

 The entire absence of feldspar is as remarkable as the abundance of large macro- 

 scopical biotites." 



This extended quotation is made to avoid repeating many details 

 already published and to bring out the bearings of the later and more 

 extended observations. Professor Zirkel also gives a good colored plate 

 of a micro-section* and several drawings of individual leucites.f 



UNPUBLISHED OBSERVATIONS OF CROSS. 



After the specimens and observations for the present paper were gath- 

 ered and fairly well worked up, the writer learned that his friend, Dr 

 Whitman Cross, had visited the Leucite hills twelve years ago, and had 

 made extended observations, amplified later by chemical analyses of the 

 rocks, with the intention of some time publishing them. On consultation 

 over the rocks it was evident that 

 in general our observations are 

 in harmony, but that each of us 

 in important points had comple- 

 mented the work of the other. 

 The writer has sought, therefore, 

 to leave untouched certain topics, 

 such as the relations of the sev- 

 eral flows, the chemical composi- 

 tion except as it is shown by the 

 analyses already published, and, 

 aside from one small sandstone 

 fragment, the matter of inclu- 

 sions or xenoliths, as Sollas uses 



the term, IOr On all these points Figure 2.— Drawing frotn a Photomicrograph of a 



Dr Cross' investigations are 

 much more complete than my 

 own, and their early publication 

 will be looked for with great 

 interest. 



Variety of Rock rich in Leucite. 



The large irregular crystals are biotite. The 

 small rods are augite. The round crystals are leu- 

 cite. The actual field was 1.2 millimeters. The 

 specimen came from the west end of the I^eucite 

 hills, at locality number 7. 



VARIETY OF ROCK RICH IN LEUCITE. 



The specimens richest in leucite of those gathered came from the west 



* Plate v, figure 4. 



f Plate i. figures 21, 22, 23. 



XXVI— Bull. Geol. Soc. Am., Vol. 8, 1896 



