1916] The Ottawa Naturalist. 61 



force or push and drag of a glacier has been supposed to have 

 produced folding and overthrusting in the partly consolidated 

 Pleistocene clays which it overrode. A single case has been 

 mentioned by Sardeson (15) in which the loosening of subjacent 

 limestone strata consequential to glaciation, has produced a local 

 brecciation. This case is not intraformational under Walcott's 

 definition, as the beds in question are Paleozoic in age, but it 

 is conceivable that the glaciation of certain surfaces might have 

 produced true intraformational breccias. It has been supposed 

 that the close and peculiar folding in certain Pleistocene clays 

 and delta deposits is the result of "drag" by grounding icebergs. 

 Whether or not these folds owe their origin to such a cause, 

 it is probably doubtful if intraformational breccias could be 

 formed in this way, owing to the peculiar consistency of the 

 sediments. The argument here against brecciation as a result 

 of intense folding and overthrusting is much the same as in the 

 case of subaqueous-gliding-deformation in clay deposits. 



Conclusions. 



The attempt has been made in the foregoing pages to 

 classify intraformational glomerates according to their possible 

 as well as probable origin. It is fully realized that the classifi- 

 cation is merely preliminary in its scope, and no attempt has 

 been made to cover all the literature on the subject. The thesis 

 has been to emphasize the importance of certain textures and 

 structures, especially in limestones, and to suggest that then- 

 systematic study may lead to a more comprehensive view of 

 the history of the seas from and under which they were de- 

 posited. Walcott was the first to define the difference between 

 intraformational and interformational conglomerates. His 



paper is important as it deals with the origin and deposition of 

 limestones, and points the way to a more careful consideration 

 of unconformity and disconformity in the field. Wherever the 

 stratigrapher finds a change in the structure of the zones, no 

 matter how superficial such change may at first appear, he should 

 be on his guard for a probable change in the conditions of de- 

 position and all the attendant geological phenomena, which 

 may hypothetically be the cause of such a change. It has been 

 pointed out that the usual rock section, as exposed by streams 

 and roads, is apt to give little or no evidence of important struc- 

 tural phenomena, such as ripple- marks, mud cracks, etc. Under 

 certain conditions intraformational limestone glomerates are 

 very difficult to detec . in the field, owing to the more or less 

 homogenous composition of the phenoclasts and cement. The 

 relation of intraformational zones to fossiliferous zones is of great 

 significance in the study of limestones, and it has been found 



