1864.] T. STERRT HUNT ON LITHOLOGY. 23 



adjacent broken silicious strata ; thus assuming for small distances, 

 the characters of an intrusive rock. For some figures and descrip- 

 tions illustrating these broken and distorted strata, see Geology of 

 Canada, pp. 21, 28. We may also allude in this connection to the 

 observations of Dr. Hitchcock amono; the altered strata of the Green 

 Mountains, which seem to show that the pebbles of gneiss and of 

 quartz in certain conglomerate beds have been so softened astohave 

 been flattened, laminated, and bent around each other. (Silliman's 

 Journal [2], xxxi, 372.) Hence, while the tendency of the various 

 observations above cited is in favor of the indigenous character 

 of many rocks hitherto regarded as eruptive, we have at the same 

 time evidence that these rocks are occasionally displaced. We 

 should not therefore on a-priori grounds reject the assertion that 

 any metamorphic sediment may sometimes occur in an exotic 

 or intrusive form. A given rock, like limestone or diorite, may 

 occur both as an indigenous and exotic rock ; and different por- 

 tions of the same mass may be seen by different observers under such 

 unlike conditions that one may regard it as indigenous, and the 

 other, with equal reason, may set it down as intrusive. It is evi- 

 dent then that to the lithologist, who examines rocks without 

 reference to their geological relations, the question of the exotic or 

 indigenous character of a given rock is, in most cases, one alto- 

 gether foreign ; and one which can frequently be decided only by 

 the geologist in the field. Hence, although generally made a fun- 

 damental distinction in classification, it will be disregarded in the 

 following sketch of the nomenclature of crystalline rocks. 



I may here allude to a fact which I have already noticed, and tried 

 to explain, (Silliman's Journal [2], xxxi, 414, and xxxvi, 220, note,) 

 that throughout the great metamorphic belt which constitutes the 

 Appalachian chain, exotic rocks are comparatively rare (at least 

 in New England and Canada) ; but abound, on the contrary, among 

 the unaltered strata on either side. Illustrations of this are seen 

 in the valley of Lake Champlain, and in its northward continua- 

 tion toward Montreal, in those of the Hudson and Connecticut, 

 and in the northeastward continuation of the latter valley by Lake 

 Memphramagog to the Bay of Chaleurs, which is marked through- 

 out by intrusive granites. In accordance with the reasons already 

 assigned for this distribution of exotic rocks, it is probable that a 

 similar condition of things will be found to exist in other regions ; 

 and that eruptive rocks will, as a general rule, be found among 



