Vol. 50.] ' DEVONIAN ' SERIES IN PENNSYLVANIA. 733 



tracing and scrutinizing the various layers of shale, sandstone, etc. T 

 and of gaining access to the innumerable and varied exposures 

 of cone-in- cone which they enclose. The Portage strata here are 

 marvellously uniform in character and composition : thin, flaggy, 

 current-bedded, pale-grey sandstones are interbedded with laminated 

 shales of various shades of purple, grey, etc., the changes from 

 one layer to another being very frequent ; but horizontally, each 

 bed, band, or layer maintains its individuality in a marked degree. 

 The shales, as well as the surfaces of the more siliceous beds, reveal 

 abundant evidence of organic life — we find trails, tracks, and burrows 

 of worms and other creeping things by the myriad ; fucoids, etc. are 

 not uncommon ; mud-flows, rill and ripple-markings innumerable, 

 besides very numerous other markings of a puzzling nature.' "While 

 a few of the sandstone-layers become thick enough here and there 

 to quarry, the shales, though often containing alum and lime, are 

 never worked. Natural gas and a little petroleum pervade the 

 strata to some extent. 



The cone-in-cone seems to occur on certain definite horizons and to 

 lie parallel with or interbedded in the shales, etc. It occurs in sepa- 

 rate patches, discs, aggregated or clustered layers or flattish cakes, 

 whose contour is round or irregular-curvilinear. Within a hori- 

 zontal distance of 100 feet one may come upon half a dozen or more 

 individual conic masses on the same plane, while imthe next 100 

 or even 1000 feet none may be found. In general dimensions 20 

 feet across or long is the size of the largest single layer that the 

 author has seen ; and individual masses more than 6 or 6| inches 

 in thickness are very scarce. In the separate layers or lenses the 

 heights of the cones never exceed about 4 inches and often run as 

 low as -£q inch : indeed, they taper or die out to nothing. Some 

 conic masses are composed of as many as six or eight separate heights 

 or zones of cone-in-cone layers one above another, no two layers 

 being of uniform dimensions, and the apices of the cones of the 

 lower layers are directed upwards, or rather towards the central 

 stratum of the mass. Very few of the layers of cone-in-cone occur 

 singly. 



The cone-structure is harder than the surrounding strata, but in 

 coloration there is practically no difference. Both upper and lower 

 surfaces of the layers of cone-in-cone often present a wavy form, such 

 as is seen in most current-bedded fissile sandstones. PI. XXXV. 

 fig. 1 shows a naturally exposed and weatherworn transverse 

 section of a characteristic aggregate of individual and separated 

 layers of the cone-in-cone in situ, forming or constituting a typical 

 Portage conic mass : in this specimen there are three separate layers 

 of cones above the nucleus or central layer. This nucleal layer lies 

 just above the dark shadow to the right of the watch. In PI. 

 XXXV. fig. 2 this specimen is drawn in diagrammatic form, in 

 order to bring out more clearly the relative position and number of 

 conic cakes revealed in the mass : it also gives point to the nucleal 

 stratum — a current-bedded stone, and the leading features of the 



1 Pennsylv. Geol. Sury., Summary Final Eeport, vol. ii. (1892) p. 1349. 



