NO. 1313. LOWER DEVONIC OF MARYLAND— SCHUCHERT. 421 



imbedded, we find, in Maryland and >^ome i)arts of Virginia, that in the friable sand- 

 stone the shells are entirely silicitied and quite free from adhering stone, so that the 

 exterior markings and internal structure are perfectly preserved; the interior being 

 quite hollow, or filled only with loose sand. In these localities, not only do we find 

 tlie cavities of large gasteropods with no more adhering matter than those of the 

 Tertiary sands, but more unfrequently the delicate internal apparatus of the Brachi- 

 opod is almost entirely preserved. 



Mr. 11. l^. Rowe" was the lirst to explain the cause for this restricted 

 leaching out of the Oriskany fossils and their occurrence in ".sand 

 pockets." He writes: 



Most of the fine collecting grounds for Oriskany fossils in this region are within 

 five or ten minutes walk from the hotels in Cumberland. The disintegration of the 

 sandstone has been carried on there much more completely than at any other place, 

 and has been due, no doubt, to the cutting of the Potomac River and Wills Creek 

 across Knobley Mountain and Shrivers Ridge. 



The constant downward percolation of the water from the Potomac 

 River and Wills Creek, when both flowed over this part of Cumber- 

 land, has carried away the calcareous material of the Oriskan}- arena- 

 ceous limestone and the fossils, and has partially replaced the latter 

 with silica. As leaching continued, all the calcareous material was 

 finally removed and more or less large, partialh" empty pockets or 

 caves were formed, filled wdth loose sand, in which the fossils are found 

 at times in considerable quantity. 



In western Maryland the Oriskanian is present in greatest volume, 

 and it continues so both to the north and south along the strike of the 

 Ciunberland Appalachian folds. Eastward the lower black shale 

 rapidly disappears, and at its most eastern outcrops the upper portion 

 is generally much reduced in thickness and the calcareous material is 

 usually absent. Here the Oriskany closely resembles the Tuscarora 

 sandstone near the base of the Ontario. The most easterly locality 

 for the Oriskany, near the old shore line, shows a depth of only 50 

 feet, while but 8 miles west, at Hancock, it is 225 feet thick. 



The thickness of the Oriskany is variable. On the W^inchester road, 

 at Pinto, the Upper Oriskany is almost entirely absent. At the Devils 

 Back Bone it also is decidedly thinner than at Ridgely. These facts 

 lend additional support to the evidence that western Maryland was a 

 land area during Onondaga time, when the Oriskan}' formation was 

 locally considerably removed. 



The small Lower Oriskany fauna thus far collected is nearly all new, 

 and the Upper Oriskany, also, has yielded a number of new forms 

 since Mr. Andrews made his collection. 



«The Paleodevonic formations of Maryland, a study of their stratigraphy and 

 faunas. A dissertation presented to the board of University Studies of the Johns 

 Hopkins University for the degree of Doctor of Philosophy, May, 1900. This thesis 

 will be published by the Geological Survey of Maryland in the volume devoted to 

 the Devonic formations. 



