104 C. D. WALCOTT — DISCOVERY OF SILl'KIAN VERTEBRATES. 



Mode of Occurrence. — The stratigraphic section shows the vertical range 

 of the fish remains to be from about 20 feet above the base of the .sand- 

 stone to its summit and one or two feet into the superjacent argillaceous 

 shale; in all, 75 to 80 feet in the Harding quarry section. The horizontal 

 distribution extends along some eight miles of outcrop west of Canyon 

 City, and another locality was discovered 150 miles to the northwestward, 

 by Mr. George II. Eldridge, on Cement peak, southeast of Crested butte, 

 Gunnison county, Colorado. Tins locality is now under investigation. 



In the Harding sandstone the fish remains are most abundant in a 

 reddish, sandy shale that occurs in irregular bands at several horizons. 

 They are also scattered irregularly through the more massive beds. Tins 

 is the ease with the chordal sheaths more than with the plates and scales. 

 The latter visually occur in great numbers with only a few traces of the 

 former, while in the massive sandstone the plates and scales are infre- 

 quent and the sheaths more or less abundant. The invasion of the sand 

 in large quantity appears to have overwhelmed the ChimseraAike fish 

 and acephalous mollusks, while the armor-plated fishes, gasteropods and 

 cephalopods, escaped to subsequently perish and have their remains 

 rolled about by the currents spreading the thinner and finer sandy layers. 

 The acephalous mollusks and the sheaths occur in the latter, but less 

 frequently. In the upper bed of coarse sandstone numerous plates and 

 fragments of plates occur, but all are more or less injured by the tritura- 

 tion of the sand as they were rolled along with it. The same is true of 

 the greater portion of the fish remains in all the shaly bands. As yet 

 no bed has been discovered where the conditions were favorable to the 

 preservation of the united plates or scales forming the armor of the fish.* 

 The chordal sheaths show less evidence of abrasion, but no other portions 

 of the same fish have been found with them. 



The invertebrate fauna associated with the fish remains is largely 

 molluscan and of sand-loving types. The exceptions to this are found 

 in the shaly beds where the rolled fragments of gasteropods and cepha- 

 lopods indicate transportation from a more congenial habitat. The 

 numerous specimens of Lingula and of lamellib ranch shells and the vast 

 number of annelid borings in some portions of the sandstones indicate 

 the conditions of the deposition of the massive layers, while the shaly 

 bands denote the period of minimum deposition and maximum accumu- 

 lation of the fragmentary fish remains and the rolled fragments of in- 

 vertebrates. 



Position in f/n geologic Series. — This has already been determined by 

 the study of the invertebrate fauna. The fish remains occur at the 

 horizon of the lower Trenton in America, or the relatively similar hori- 

 zon, the lower Bala of Wales. 



* A single specimen of Axtraspi* d* tid< r<it*i has liccii i'oii ml since this paragraph was written (p. LC7). 



