36 Geology, l^c. of the Connecticut. 



and imperfect characters prevented my putting it down as a 

 distinct rock. The stage road from Greenfield to Brattle- 

 borough passes over it in the southern part of Guilford. At 

 the same place occurs well characterized chlorite slate ; but 

 not constituting any extensive range. 



One mile south of this spot, another rock occurs, which an 

 observer, at first sight, would pronounce to be granite. It 

 is unstratified* and has the color of granite: but seems to 

 be made up chiefly of quartz with a little mica interspersed. 

 It seems to be an aggregate to which no particular name has 

 as yet been aj^plied; although the proportion of mica is so 

 small that it might almost be called quartz simply. It ap- 

 pears to form a large bed in argillite, or talco-argillite. 



The strata of argillite, both in Connecticut and Vermont, 

 run in a direction nearly N. E. and S. W. and are highly in- 

 clined, generally varying hut little from perpendicular. They 

 are undoubtedly primitive — that is, the evidence of this is as 

 great as in regard to the mica slate; both being highly inclined, 

 and destitute of organic remains. Indeed, Bakewell, who has 

 transferred argillite to the transition class, says " mica slate 

 has a near affinity to clay slate ; and as I have arranged the 

 latter with rocks of the second class, it may perhaps be doubted 

 whether mica slate should not also have been transferred to 

 the same class.'' (Geology p. 83.) Do we not here see to 

 what temptations the system maker is exposed, when pres- 

 sed with difficulties.^ However, as Professor Kidd remarks, 



*"By stratificatien we understand the divisions of a mass of rocks into 

 many parallel portions whose length and breadth greatly exceed their thick- 

 ness." JVorth-Jimerican Rev. .IVo. 29, p. 232. 



"Where a rock is stratified, is it necessarily bounded by parallel surfacei? 

 If so, let us hear no more of mantle-shaped, saddle-shaped, basin-shaped, 

 trough-shaped stratification." Greenou^h''s Geology, Essay 1. 



I would beg liberty to enquire, whether some of these difficulties might 

 not be removed by defining stratification lo be the division of a mass of rock 

 into many parallel or concentric portions ? But after all, this, like a thousand 

 other definitions in natural history, is only an approximatiom to the truth : 

 For if mathematical exactness be essential, we have never yet seen any rock 

 whose divisions were either parallel or concentric. Bakewell'a distinction 

 (Geology p. 31.) between "the structure which is caused by chemical agen- 

 cy, or by crystallization, and mechanical depositions," would perhaps give 

 relief to some of the difficulties in regard to stratification, were geologists 

 agreed what rocks have a structure caused by chemical agency and what 

 ones are mechanical deposites. But they are not agreed on this point, as is 

 evident from the very example he brings to illustrate his principle, whea 

 he says, that the division of slate rocks into laj^ers, is the result of their chem- 

 ical composition. 



