GEOLOGY. 457 



wards broken up into the present areas by a number of axes of eleva- 

 tion, or else by great faults. 



Dana has since reviewed this subject at some length and takes a dif- 

 ferent view. He remarks that Cook's supposed area, 1 ,000 miles or more 

 in length, of Mesozoic sandstones, now covering regions that are 1,000 

 feet or more above sea-level, must either have been marine or lacustrine, 

 neither of which conclusions is in accordance with what we know of 

 the rocks in question. Those of the Connecticut valley are appar- 

 ently of fluvatile and estuary origin, and the same is probably true of 

 other areas. The deposits of coarse and fine material, as long since 

 pointed out by Edward Hitchcock, came from rocks bordering on the 

 existing areas, and show that the basin could not have extended much 

 beyond its present limits. The materials bear evidence, in the distri- 

 bution of materials of varying coarseness, of alternate swift and slow 

 currents. The coarser sediments are most common along the borders of 

 the present areas, where, however, they occur interruptedly. 



In all these respects their distribution corresponds to that of the 

 latter valley-deposits of the Connecticut River. The elements of the 

 sandstones are the result of mechanical disintegration of the crystal- 

 line rocks of the margin, including not only quartz but undecayed feld- 

 spar, suggesting, as remarked by Dana, a disintegration of the adjacent 

 crystalline rocks. He notes in this connection, that " disintegration 

 by the rusting of the mica (biotite) is now making (to the east of New 

 Haven), just such granitic sand as constitutes the coarse (Triassic) sand- 

 stone of East Haven." Dana compares the material of the Trias of the 

 Connecticut valley to the stratified drift of post-Pliocene age in the same 

 valley, and conceives these Mesozoic sandstones and conglomerates to 

 have accumulated in a great estuary in a glaciated region. The various 

 Triassic areas are parallel to old lines of uplift, which in Pennsylvania 

 correspond to the sigmoid form of the ancient topography. This great 

 area was distinct from that of the Connecticut valley. 



SERPENTINES AND RELATED ROCKS. 



The question of the geological age and the origin of serpentines 

 was discussed in the report for 1882. The present writer has since 

 published an extended memoir on serpentines, repeating with detail 

 many of the facts there noticed, and recalling the history of the ser- 

 pentines as found at various geological horizons in the Laurentian, 

 the Huronian, the Montalban, and the Taconian series, as well as the 

 later development of it in the Silurian, in the remarkable bed of serpen- 

 tine formerly exposed among the dolomitic strata of the Onondaga salt- 

 group at Syracuse, K. Y. He has noticed the serpentine associated 

 with limestone in the Laurentian series at New Eochelle, N. Y., where 

 it occurs, both mingled with limestone, forming varieties of ophicalcite 

 like those common elsewhere in the Laurentian, and also constituting 



