No. 2.] DANA — SOME POINTS IN LITHOLOGY. 85 



eruptive masses — shows that the special conditions producing 

 augite, instead of hornblende, whatever they are, have often acted 

 on a vast scale in the earth's history. And so, also, the very 

 wide distribution of hornblendic rocks, especially among the meta- 

 morphic kinds, is evidence of a like comprehensive influence of 

 the conditions needed to make hornblende in place of augite. 

 The geological importance of the distinction is reason enough for 

 recognizing it in lithological systems. 



8. Massive or Schistose. — Massive structure is often made 

 prima facie evidence of igneous origin. Granite, with hardly a 

 questioning thought, has usually been placed solely among erup 

 tive rocks. The igneous origin of dioryte even now is hardly left 

 open to investigation by some litholigsts. Serpentine has been in 

 the same category, though at present there are advocates of its 

 metamorphic origin. And so other massive rocks are too likely- 

 to be set down as eruptive without a fair investigation. No two 

 rocks are put farther apart in some lithological systems than 

 granite and gneiss; and yet. none are more closely related in 

 constitution and all essential characteristics. 



The following are reasons for disregarding this distinction of 

 massive or schistose in classifying rocks, and for allowing a 

 massive structure little weight in deciding the question as to 

 eruptive or metamorphic origin. 



(1.) Massive rocks maij be both metamorphic and eruptive. — 

 Granite, syenyte, with dioryte and other hornblendic rocks, are 

 examples of massive rocks that are of both modes of origin. 

 Many localities where kinds of these rocks occur metamorphic 

 have been described. I will mention two or three from the 

 many I have observed in New England, (a) Ten miles east of 

 New Haven, Connecticut, in a railroad cut at Stoney Creek, a 

 bed of granite, having a small northward dip, changes gradually 

 to gneiss, and then to gneiss with some very micaceous mica 

 schist, so that within thirty yards from east to west these three 

 rocks are found constituting the same bed ; and the granite is a 

 part of the general gneissic formation of the region. (6) The 

 labradorite-dioryte two miles west of New Haven graduates 

 rather abruptly above and below, and also laterally, from a 

 massive rock into a slaty chloritic mica schist, and does this so 

 often and variously, that there is no reason for questioning its 

 metamorphic origin, (c) A hornblende (or actinolite) rock, just 

 north-east of Bernardston, of a massive kind, occurs among thin 



