380 



SCIENCE 



[N. S. VoL.XXVni. No. 716 



The sections of the Catalina rocks show a 

 great variety of mineral composition rang- 

 ing from quartzite to muscovite-schist and 

 biotite-schist. There can be little doubt of 

 their elastic origin, though they are now pene- 

 trated by layers of pegmatitic granite, which 

 partake of the deformation. 



These gneissic and schistose roclis are mem- 

 bers of the series of pre-Cambrian schists for 

 which I proposed the name " Arizonian." 

 They are widely distributed in middle and 

 southern Arizona and offer an inviting field 

 for investigation. 



Wm. p. Blake 



Tucson, Aeizona 



physiographic sketch of lewis county, n. y. 



The county of Lewis, bounded on the 

 northeast by St. Lawrence, on the west by 

 Herkimer, on the south by Oneida and on the 

 ■ east by Oswego and Jefferson counties, ex- 

 tends from the 43° 25' of northern latitude 

 for fifty-four miles northward and from the 

 75° 50' western longitude for nearly thirty- 

 four miles to the east, and is naturally di- 

 vided by Black River into two heterogeneous 

 sections from a genetic point of view, an 

 eastern section, made up to the greatest ex- 

 tent of igneous and metamorphic rocks, and 

 a western one that chiefly comprises a sedi- 

 mentary series. 



Successive manifestations of dynamical 

 forces upon the igneous rocks in the east, as 

 the crushing of the granites into gneisses and 

 the intrusions of syenites, as well as gabbros, 

 into the gneissic series and into the crystal- 

 line limestone series, have affected also to 

 some extent the sedimentary rocks in the west 

 in such a manner as to slightly bend during 

 post-Ordovician time Cambrian, Ordovician 

 and (Lower) Silurian strata into a flat syn- 

 clinal fold that plunges at a very small angle 

 to the north-northeast, while subsequent 

 erosion nearly completed one of its cycles by 

 reducing post-Ordovician topography to a 

 peneplain, remnants of which can still be 

 traced in the most elevated portions of the 

 western section. 



During another cycle of erosion that was 



never completed, but only brought about the 

 partial destruction of the peneplain and ex- 

 posed in succession the different members of 

 the Ordovician, i. e., the Black River and 

 Trenton limestone, as well as the Utica- 

 Frankfort slates and the Pulaski sandstone 

 shales, at least one member of the Silu- 

 rian, namely the Oswego sandstone, and, 

 bordering the Ordovician in the east, the 

 Potsdam sandstone of the Cambrian, a strike 

 fault west of Black River, extending through 

 the entire length of the county and pos- 

 sibly beyond, caused the disappearance of 

 the Potsdam sandstone along the fault line, 

 thus bringing the pre-Cambrian igneous and 

 metamorphic series into contact with the 

 Ordovician. 



Succeeding the faulting of the region and 

 the invasion of ice sheets of local character 

 from the Adirondack, as well as from the 

 Lake Ontario region, which led to the for- 

 mation of two distinct sets of ground and 

 terminal moraines, a second flood plain was 

 established, adjacent to the former, but on a 

 much lower level, which we might consider a 

 base-leveled plain, as its uniformity of level 

 is admirable for its entire extension from the 

 utmost northwestern points of the county for 

 over forty miles, as far as Forestport, beyond 

 the southern boundary line of Lewis County. 



Into this flood plain post-glacial erosion 

 has sunk in several successions, of which two 

 are more prominently marked by river-ter- 

 races, the channel that is now occupied by 

 Black River, and has modified the topography 

 of the regions east and west of Black River 

 to such an extent as to impart to them the 

 physiognomy of uplands and highlands, re- 

 spectively. 



At present the area under discussion is 

 passing through a cycle of erosion that has 

 started recently, speaking geologically, and 

 conditions have been established that appar- 

 ently favor the rejuvenation of the entire 

 drainage system of the region and the carv- 

 ing into the sedimentary strata in the west 

 along joint planes and into the igneous and 

 metamorphic rocks in the east without special 

 regard to basal structure, of those deep gulfs 



