74 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



area the simulating residual shale will be traced to merely dull laminated 

 limestone or calcareous shale. 



A characteristic weathering product of the lower half of the Elbrook is 

 light colored, sometimes almost white, waxy translucent chert approach- 

 ing chalcedony in appearance and structure. This appears in the soil in 

 small fragments, usually only a few inches thick with more or less rounded 

 edges. The color of this chert is sometimes a light yellow or even light 

 red, but it is never black nor banded like the Tomstown chalcedonic chert. 



AGE AND CORRELATION. Fossils have been found only in the basal 

 limestones of the formation in the vicinity of Waynesboro, Pennsylvania. 

 These consist mainly of well-preserved heads and tails of two species of 

 trilobites, one of which, a species of Dolichometopus, is not uncommon. 

 These trilobites belong to new species whose age relations have not been 

 definitely determined. However, as they are closely allied to species 

 known to be characteristic Middle Cambrian fossils it seems highly prob- 

 able that the Elbrook is of similar age. 



THE CONOCOCHEAGUE LIMESTONE 



On the northwest, north and east flanks of the Adirondack uplift the 

 Potsdam sandstone grades upward through passage beds into a limestone 

 to which Ulrich and Gushing have applied the name Hoyt limestone. 

 This is succeeded by a massive dolomite known as the Little Falls dolo- 

 mite. Fossils have been found in all three of these formations, but are 

 reasonably plentiful only in the Hoyt limestone. The fauna of this 

 limestone was first procured and in part briefly described by Walcott 

 many years ago. Recently the same authority revised and completed his 

 studies of the Hoyt and Potsdam faunas, the results being published in a 

 small monograph. As now known these early New York " Saratogan " 

 faunules comprise, besides a number of trilobites and shells of various 

 kinds, large concentrically laminated masses in reef -like aggregations. 

 These masses are thought to be calcareous algae. Two species are dis- 

 tinguished, one having been described by Hall under the name Cryptozoon 

 proliferumj the other is a related new species. These two species have 



