

B1GSBY PALEOZOIC ROCKS OF NEW YORK. 395 



to constitute a systematic break, except at one place — the Oriskany 

 Sandstone, the base of the Devonian in New York, — there being no 

 break of like importance at the Oneida Conglomerate period, contrary 

 to an opinion towards which able geologists are now inclining, — 

 an opinion which leads them to consider the break at the Oneida 

 Conglomerate as systematic. 



3. All the palaeozoic groups of New York slowly pass one into 

 the other by gradation of mineral and organic characters, with 

 easily-explained exceptions. 



4. The palaeozoic strata of New York are comparatively thin. 

 They seem to have lost in thickness what they have gained in ex- 

 tension. 



5. De Verneuil rightly divides the New York groups into two 

 great classes, — the " constant" and the " local." Among the former 

 are Potsdam Sandstone, Trenton Limestone, and Niagara. Among 

 the latter are the four lower Helderbergs, and perhaps Oneida Con- 

 glomerate, &c. This is a useful division. 



6. That it is both convenient and natural to divide the Silurian 

 and Devonian systems of this State each into three stages, — the 

 division being based on change of sediment and their fossil contents. 



7. The Middle Silurian stage is a period of especial transition — 

 from the coarseness of some of its sediments, from their innumerable 

 and minute alternations, and from the organic poverty prevailing. 



8. That the presence of Oneida Conglomerate in New York does 

 not necessitate a change of name for all the strata below it (of " Cam- 

 brian" for instance); because a conglomerate does not always indicate 

 systematic change, — not even if there be volcanic intercalation, pro- 

 vided there is conformableness, and some community of fossils. 



The Oneida Conglouierate seems to be local, is supernumerary, and 

 only found at present on the east of Middle North America. 



9. The hardening and crystallizing effect of metamorphism is seen 

 only in the neighbourhood of hypogene rocks. 



1 0. The New York basin exhibits few uplifts, and those of limited 

 magnitude ; no uplifts dividing it into a series of deep basins con- 

 tained in hypogene beds, as in Bohemia, Wales, &c. Neither has it 

 sheets of alternating volcanic grit (conformable), save in the Potsdam 

 Rock on Lake Superior. 



This basin has a "lay" or position of its own, as a number of undu- 

 lating sheets of sediment, dipping slightly to the south-west, here and 

 there pierced by a peak of crystalline rock, and in certain regions 

 raised into three broad low domes of great length. 



1 1 . The sedimentary rocks of this basin have submitted to two 

 kinds of plutonic disturbance, independent of each other, and act- 

 ing at distant intervals : 1st, that of secular or slow oscillation during 

 deposition ; 2nd, that of disturbance arising from paroxysmal uplifts 

 long after their completion. 



12. The whole Silurian and Devonian series of strata having, 

 during deposition, sunk to the depth of 13,300 feet, it is submitted 

 as a query whether it does not seem necessary to suppose that they 

 were elevated into their present position by the post-carboniferous 



VOL. XIV. PART I. 2D 



