270 F. D. Adams — Melilite-'bearing Bock. 



tions served to indicate the relationship of the rock although 

 in this particular specimen the melilite had been almost 

 entirely destroyed by decomposition. This rock was therefore 

 in the last edition of Prof. Kosenbusch " Massigen Gesteine," 

 page 809, classed with that from Alno as Alnoite, a dike rock 

 corresponding to melilite basalt among the effusive rocks. 

 As a new occurrence of a rare and curious rock it seemed 

 worthy of careful study, the more so as it is, so far as I am 

 aware, the first melilite rock that has been found on this conti- 

 nent. 



The locality has therefore been revisited and a number of 

 specimens of the fresh rock obtained from several large blocks 

 which were thrown out on the slopes of the cribwork defining 

 the channel. The dike itself of course cannot be seen, as it 

 lies in the bed of the river and is now under several feet of 

 water and but little fresh material can be obtained even from 

 the blocks, as these are for the most part much decomposed. 

 The strike of the dike would carry it through the village of 

 Ste. Anne, but although the Potsdam sandstone is exposed in 

 a number of places in the village no trace of the dike could 

 be found, nor could any similar rock be found elsewhere in 

 the vicinity. 



The rock has a fine grained grayish-black grounclmass 

 through which are usually distributed large phenocrysts of 

 biotite, olivine generally of a bright red color but sometimes 

 green and black pyroxene. These are generally plentiful and 

 sometimes so abundant as to constitute the greater part of the 

 rock, giving it a very striking appearance. Some of the 

 rock is almost free from these phenocrysts and consists of the 

 fine grained groundmass alone, which in such cases is almost 

 invariably much decomposed. It was impossible to ascertain 

 whether this variety of the rock is confined to any particular 

 part of the dike. The phenocrysts sometimes measure as 

 much as 4 or 5 centimeters across but are generally somewhat 

 smaller, 1\ centimeters being the usual size. The biotites are 

 frequently arranged in a rudely parallel position coinciding, as 

 in the Swedish rock, with the direction of the walls of the 

 dike, thus giving the rock a sort of schistose structure in this 

 direction. The groundmass, which can only be studied prop- 

 erly in thin sections of the freshest material, is composed of 

 smaller biotites, olivines and pyroxenes between which lies a 

 still finer grained aggregate made up of individuals of melilite 

 and little pyroxene spicules, the relative proportions of the two 

 minerals varying considerably in different parts of the rock. 

 Magnetite often in little cubes and octahedra occurs somewhat 

 abundantly in the groundmass as well as in the form of inclu- 

 sions in almost all the other constituents of the rock. Pyrrho- 



