192 C. D. WALCOTT — INTRA-FOEMATIONAL CONGLOMERATES. 



has been done and observations extended, with the result that I find 

 the presence of intra-formational conglomerates a not uncommon phe- 

 nomenon, one that must receive the attention of every field geologist 

 working in the Appalachian region, from the Saint Lawrence valley in 

 the northeast to the Cretaceous boundary of the Paleozoic of the far 

 southwest in Georgia and Alabama. 



Care is to be taken that intra-formational breccias are not confused 

 with the intra-formational conglomerates. The former have a wide geo- 

 graphic distribution, and owe their origin to local disturbance within 

 the beds affected, without presupposing elevation above sealevel and 

 erosion. 



Intra-formational Conglomerates. 



Definition of Term and IlUistration. — An intra-formational conglomerate 

 is one formed Avithin a geologic formation of material derived from and 

 deposited within that formation. An illustration occurs in the old lime- 

 stone quarries on the east shore of the Hudson, below Schodack landing, 

 Rensselaer county. New York. The section is formed of thinly bedded 

 limestone, carrying the typical Olenellus fauna. Toward the summit of 

 the quarry a band of conglomerate limestone rests conformably on the 

 bedded limestone. Pebbles and fragments of several varieties of lime- 

 stone occur, in which fragments of typical species of the Olenellus fauna 

 were found. The conglomerate band varies in thickness from 2 to 6 feet, 

 and it is capped by thinly bedded limestones that carry the same species 

 of fossils as the limestones beneath the conglomerate and the bowlders 

 in the conglomerate. It shows that the limestone pebbles, bowlders and 

 brecciated fragments were formed from a calcareous sediment sufficiently 

 consolidated to be broken up, more or less rounded by attrition and col- 

 lected to form a bed of conglomerate, the matrix of which is usually 

 calcareous. This section clearly proves the formation of conglomerate 

 within the Lower Cambrian terrane, the materials of which were derived 

 from limestones deposited during Lower Cambrian time. 



The conglomerate at the locality described is not as clearly marked as 

 some in the Lower Cambrian terrane of Lancaster and York counties, 

 Pennsylvania, and in the conglomerates at the base of the great Ocoee 

 series of Tennessee. The limestone conglomerates of the Cambrian and 

 Ordovician of the Saint Lawrence valley are not typical illustrations of 

 true intra-formational conglomerates, but I shall speak of them, as they 

 appear to have been formed under somewhat similar conditions. 



Canadian Localities. — Sir W. E. Logan has graphically described the 

 limestone and conglomerates of the south shore of the Saint Lawrence 

 at Trois Pistoles, Bic, Metis, the vicinity of Quebec and the west coast of 



