150 C. L. WHITTLE — METAMOE.PHIC CONGLOMERATE. 



The extreme mobility of the ottrelite-bearing solution is indicated by 

 the manner in which the ottrelite needles have insinuated themselves 

 into included feldspar grains along no visible lines of fissuring. 



Mineralogic Constituents. — As in all described occurrences of this min- 

 eral, an abundance of inclusions exists. It is noticeable that, while quartz 

 and occasionally feldspar are included, sericitc. which is the principal 

 micaceous constituent of the rock, is seldom enclosed by the growing 

 ottrelite. but may be wholly or in ]>art the nucleus about which an ag- 

 gregate formed. Such nuclei seem in some cases to have governed the 

 growth of the ottrelite. There was a tendency as the mineral formed for 

 the plates to orient themselves parallel to the sericite nucleus, so that 

 when such a nucleus is surrounded by basal ottrelite it is apt to be basal 

 also. Whether this is another example of parallel growth or is acci- 

 dental I cannot state definitely. By far the most abundant interposi- 

 tions are a multitude of extremeW minute black to brown dots and 

 aggregates. With a number 7 objective these are resolved, in the main, 

 into rutile, occurring in knee-shaped and heart-shaped twins, but gen- 

 eralh r in rounded forms, in which twinning is not distinguishable. In 

 other cases the highest objectives are incapable of individualizing the 

 grains, as is mentioned by Renard* In some crystals the rutile is 

 grouped in reticulated lines conforming rather rudely to the planes of the 

 two principal cleavages, but as a rule it is grouped along irregular lines 

 that traverse the ottrelite and the groundmass alike. It may have been 

 arranged originally in structural lines, developed along planes of bed- 

 ding, that afterward were built into the ottrelite with total disregard of 

 any observed relationship, in the same manner that quartz and feldspar 

 droplets were built into albites in another phase of this rock. Other 

 inclusions are graphite (determined by deflagration) and little coffee- 

 brown ilmenite plates (titaneisen glimmer). A powerful current from 

 an electro-magnet applied to that portion of the powdered rock which 

 ran through a 120-mcsh sieve attracted but a little of the particles, so 

 that magnetite and probably ferrous oxide are absent. The usual test 

 for titanium gave a positive reaction. 



As in biotite and chlorite, pleochroic zones about crystals of zircon are 

 very common in the ottrelite, and their characteristic dependence of 

 maximum pleochroism upon the maximum pleochroism of the enclosing 

 mineral is observable. While zircon usually occupies the centers of these 

 zones, other zones occur having no perceptible associated inclusion."f 



♦Researches sur la Composition et la Structure des Phyllades Andennes. Phyllade i »ttrelit6fere 

 do Montherme. Bulletin du Mus6e D'Hist. Nat. de Belgique, vol, 3, 1884-85. p. 252. 



1 1 am disposed to refer the brown material making these z ss to minute rutile grains. < ittre- 



lite containing such zones was subjected to the temperature of a Hansen burner withoul destroy- 

 ing them, so they are probably of a mineralogic nature. 



