4G2 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



the L'tica and Lorraine, or all above the supposed Utica, just above the, 

 limestone, with the" Hudson River group,'' of the New York Survey. As 

 the latter occurs out in the valley it contains a strongly marked grap- 

 toliiir fauna, usually called Normans Kill fauna. This fauna is con- 

 sidered by Prof. Lapworth to be of about Trenton age and pre-Utican— 

 a view sustained by Mr. Ami in his studies at Quebec and by Dr. 

 Gurley in his review of the graptolitic faunas. Certain it is that the 

 graptolitic fauna is not the same as that of the l'tica shale of the 

 Mohawk Valley, as has been advanced by Hall, Whitfield, and Walcott. 

 The term Hudson has been applied to these beds between the Lower 

 Heidelberg limestone and the supposed Trenton limestone beneath, 

 and the Lorraine and Cincinnati formations correlated as equivalent. 

 This can not be done logically to-day, for the series of shales and sand- 

 stones, with occasional interbedded lentiles of limestones, includes all 

 the formations from the Calciferous to Lorraine inclusive. Lt is, as 

 stated by Sir William Logan, practically the equivalent of the Quebec 

 group, although it includes more at its upper limit in taking in the 

 Lorraine strata beneath the Lower Helderberg limestone. 



The sedimentation on the outer limits of the eastern side of the valley 

 includes the Berlin grits and great thicknesses of interbedded purple 

 shales, and again red and green slates with dark argillaceous shales, 

 carrying the Normans Kill graptolitic fauna. Lentiles of limestone 

 occur bedded in the shales, in which the Calciferous, Chazy, and Tren- 

 ton faunas are found— sometimes one or two in the same lentile, as in 

 Washington County, New York. On the east side of the Hudson 

 Valley 5,000 feet of shales, slates, sandstones and limestones, of very 

 irregular succession, may be referred to the Hudson terrane. 



The evidence now at hand leads to the conclusion that in the valley 

 of the Hudson, or the northern portion of the Appalachian trough, the 

 sedimentation, from the Upper Cambrian to Lower Helderberg time, 

 was unlike that of the region to the westward. It was greater in 

 quantity and variety, and during Trenton time a graptolitic fauna was 

 buried in it, such as is unknown elsewhere in New York and the south- 

 ern Appalachians, although present in Arkansas and Nevada, All 

 attempts to correlate the Hudson series with sections elsewhere must 

 be more or less defective, except that the great mass is of Lower Silu- 

 rian (Ordovician) age. The best region to study the Hudson series is 

 from Fort Edward, above Albany, to the vicinity of Catskill. 



In Dutchess County, opposite Kingston, the Lower Cambrian quartz- 

 ite rests on the Algonkian gneisses, and the stratigraphic section is 

 represented from this horizon to the Trenton and Lorraine. South of 

 Poughkeepsie, on the east side of the river, the sedimentary beds are 

 crowded out to the river by the pre-Cambriau rocks, and below Newburg 



