400 J. E. Hyde — Desiccation Conglomerates. 



Art. XLIII. — Desiccation Conglomerates in theCoal-measnn s 

 Limestone of Ohio;" by Jesse E. Hyde. 



The occurrence of conglomeritic layers of limestone of 

 greater or less thickness in the midst of a limestone formation 

 is not uncommonly noted. They consist of fragments of lime- 

 stone ranging in size from small shot to great bowlders several 

 feet in diameter which may be either rounded or angular. In 

 some instances the source of the pebbles has clearly been a 

 regularly bedded limestone lying conformably immediately 

 below the conglomerate, in others the beds which have fur- 

 nished the material lie somewhat lower with the intervention 

 of other strata. In many cases the conglomerate can not be 

 supposed to represent a period of elevation, erosion and subsi- 

 dence of any importance, that is, a true geological hiatus. In 

 typical cases in mind they occur within the formation, there 

 being no notable lithic or faunal differences between the under- 

 lying and overlying parts. They may occur singly and at 

 widely separated intervals or in considerable numbers and only 

 a few feet apart and may range in thickness from a fraction 

 of an inch to several feet. 



Dr. C. D. "Walcott has described a number of examples of 

 such conglomerates in rocks of Cambrian andOrdovician age and 

 has applied to this type of deposit the name intra-fovmational 

 conglomerate. According to his definition of the term, "an 

 intra-formational conglomerate is one formed within a geologi- 

 cal formation of material derived from and deposited within 

 that formation.""!" In all of his examples where the thickness 

 is mentioned the conglomerate is from two to ten feet or even 

 more in thickness, and contains beside the smaller fragments 

 many large ones or " bowlders," the sizes of which are not 

 always stated but which in many cases range from two to six 

 feet in diameter. Their origin is puzzling to say the least and 

 Dr. Walcott's explanation is the only one that has been proposed, 

 so far as is known to the writer. 



"The presence of the conglomerates above the limestone beds, 

 from some portion of which they were derived, leads me to 

 believe that the sea bed was raised in ridges or domes above 

 the sea-level, and thus subjected to the action of the seashore 

 ice, if present, and the aerial agents of erosion. From the fact 

 that the limestones upon which the conglomerates rest rarely, 

 if ever, show traces of erosion where the conglomerates come 

 into contact with them, the inference is drawn that the debris 



* Published by permission of Dr. J. A. Bownocker, State Geologist of Ohio. 



\ Bull. Geol. Soc. Am., v_ol. v, pp. 191-198. The same paper without 

 modification and with a slight addition was reprinted in Bulletin 134 of the 

 United States Geological Survey, pp. 34-40. 



