512 J. A. DRESSER IGNEOUS ROCKS OF EASTERN QUEBEC 



mountain appears as the next prominent point along the serpentine belt, 

 although that belt is almost continuous throughout the distance. The 

 mountain rises 1,400 feet above the neighboring land, or 2,400 feet above 

 mean sealevel. 



This mountain, as far as known, is a mass of much altered diabase. 

 Near the eastern edge of the summit the diabase passes into a rock in- 

 termediate between hornblende granite and diorite, which may be tenta- 

 tively classed as a granodiorite. The transition is a rather sharp one, 

 a distance of a few yards only separating typical specimens of the two 

 rocks. The granodiorite seems to form only a small body, and is prob- 

 ably the residual filling of the neck of the volcano which gave rise to the 

 mass of the mountain. 



Moose mountain, in the township of Cranbourne, beyond the north- 

 eastern limit of this map, is thought to belong to this series, although 

 there is not much definite evidence concerning it yet available. A spec- 

 imen from a spur of the mountain in the township of Frampton is a 

 porphyrite — a not uncommon marginal phase of these rocks — and as 

 Doctor Ells reports the mountain to be intrusive in its relation to the 

 sediments of the district, it may apparently be safely correlated with the 

 present series. 



Eocks very similar to those of Orford have been described from Adstock 

 mountain, and also from the township of Potton, by Dr F. D. Adams.* 

 Doctor Adams found a specimen from the summit of Adstock to be a 

 diabase, and one from another part of the same mountain to be a diorite, 

 both being much altered rocks. Concerning the latter he writes : 



It is rather coarsely crystalline, massive, and of a grayish-green color, and 

 is composed of hornblende and plagioclase. The hornblende is green, or, in 

 some places, brownish in color, and is distinctly pleochroic. . . . It is 

 often twinned. Much of the hornblende is decomposed to chlorite. In manj 

 cases the alteration appears to pass through an intermediate stage in which 

 the hornblende assumes a very finely fibrous appearance. The fibers are gen- 

 erally approximately parallel, but do not as a general rule extinguish simul- 

 taneously. Individual fibers can often be seen to have an extinction inclined 

 at a small angle to their longer axes. Some of these fibrous grains show a 

 distinct biaxial figure. The plagioclase is dull from incipient decomposition, 

 but generally shows well defined poly synthetic twins, of which two sets are 

 frequently present crossing one another. Although the two minerals have 

 interfered with each other in crystallizing both show good crystal forms. 

 The feldspar is perhaps upon the whole the better crystallized of the two. The 

 fibrous hornblende is found everywhere to be mixed with chlorite. 



* Op. cit. 



