Report of the State Geologist. 255 



The fragments of the original lava are little altered. The honi- 

 l^lendes are either not at all, or but slightly bleached at their border. 



In one case a hornblende has changed to a matted mass of actinolite. 

 The pyroxenes are not changed. Small olivines are changed to fibrous 

 matted serpentine. In one case deep brown geniculate rutiles are 

 perched upon the actinolite and enveloped in the calcite. 



It is interesting to see this actinolite felt cementing minute fragments 

 of the lava and separate crystals of the basaltic hornblende and 

 pyroxene. The abundance of calcite favors the process and the lime 

 feldspars and actinolite have crystallized abundantly under circum- 

 stances which permitted the simultaneous crystallization of calcite and 

 left the amorphous ground mass and the primary constituents of the 

 lava quite intact. 



Several years ago I described some contact rocks and dyke rocks 

 resembling these, from the border of a great dyke of elteolite-syenite 

 in the north of Xew Jersey, and a comparison of these rocks led me 

 to suspect the presence of nepheline in these specimens, but I could not 

 find it with certainty. 



Mr. J. F. Kemp has described* a remarkable erratic from Aurora, 

 Cayuga Co., X. Y., which is of exactly the same character as the rock 

 here described, except that it is not accompanied by contact forms. 



It is there assigned to the nepheline-bearing dyke rocks free from 

 oliWne, to which the name fourchiie has been given, although no 

 nepheline has been found in the rock. Some of the slides examined by 

 me would admit of this assignment. In others several olivine crystals 

 occur in a single slide, and the rock would then be called monchiquite, 

 or since both forms contain hornblende, they would be called hornblende 

 fourchite or hornblende monchiquite, according to the same rather over- 

 loaded nomenclature. 



Prof. Kemp surmises that his rock may have come from the A).'chaean 

 areas to the north. From the present occurrence a nearer source of 

 "both erratics is probable. 



* American Journal of Science, Vol. XXin, Chap. III. 1882, p. 302. 



