68 GEOLOGY OF THE SECOND DISTRICT. 



do not preserve litliologically a unity of character : the one is a mixed or compound rock, 

 and described as being composed of certain minerals ; the other as a homogeneous mass ; yet 

 the fonner is not composed always of the same elements or minerals, nor is the latter always 

 a homogeneous rock. These remarks are made in consequence of having observed a remark- 

 able variation in the characters of serpentine in the Northern District of New- York, from those 

 which belong to Massachusetts and the other New-England States ; and I may go farther, 

 and say that some remarkable differences appear in the same rock, though in the same neigh- 

 borhood, as will be seen in the sequel. 



Serpentine is usually green, variegated with spots, deep or pale, and often beautifully mot- 

 tled. The green is the most common color ; still it is sometimes brown, red, yellow, and 

 veined with substances of different colors. So, upon the whole, it presents an unusual com- 

 bination of characters. It is also one of the most close grained and compact rocks we have. 

 That variety which is associated in New-York with limestone, is usually perfectly compact 

 and translucent ; that which occurs in the iron ore beds, approaches to a shaly or shivery 

 mass. Other beds, in other sections of country, as those of Middlefield and Chester in Mas- 

 sachusetts, are finely granular, quite opake, and mostly uniform in color. Varieties with 

 still greater differences are found, some of which are brecciated, as those, for instance, which 

 underlie and penetrate in various ways the beds of peroxide of iron in Jefferson and St. Law- 

 rence counties. This curious and interesting variety contains angular pieces of quartz, from a 

 tenth to half an inch in diameter. Generally they appear closely invested with the serpentine ; 

 but sometimes they may be removed, and in fact fall out of their own accord by disintegra- 

 tion. The masses of quartz are angular, and show no appearance of being incorporated with 

 the rock ; for this reason, it is quite difficult to offer a satisfactory solution of the question of 

 the origin of this quartzose serpentine. 



There has been much discussion of the question of its stratification, and there are able 

 geologists enlisted on both sides. Macculloch and Prof. Hitchcock maintain the doctrine that 

 it is often at least a stratified rock, and Prof. Hitchcock goes so far as to give the dip of the 

 strata ; but having often examined the locahty in Middlefield, the one referred to by the Profes- 

 sor, I have never been able to satisfy myself of the fact itself.* I am sensible that serpentine 

 is often in splintery or shivery masses, putting on somewhat the appearance of a shaly struc- 

 ture ; yet I have not regarded it at all as due to stratification, or even a tendency thereto. The 

 same splintery sharp-edged variety occurs in the ore beds of the north ; and often these sharp 

 pieces are striated, as if rubbed against each other, and it appears to be analogous to the glazed 

 slate in the Champlain groups, whicli I have supposed to have been pressed strongly when 

 in a yielding state, and perhaps elevated at the same instant. So serpentine, after a consolida- 

 tion at numerous points, might be exposed to pressure ; and when forced upwards, the harder 

 masses would slide upon the softer ; and by this movement, they would receive those impres- 

 sions, or stria, which appear on those glossy surfaces termed slickensides, and at the same 

 time give them that splintery sharp-edged condition in which we now find the mass. 



* Hitchcock's Geological Reporl of Massachrisells, Vol. 2. p. C16, 



