Prof. Dr. Pavloic — Oligocene Sandstone in Neoeonuan Clays. 53 



older or newer than the rock which encloses it. The facts are that 

 the clay cut by the dike is of Lower Cretaceous age, while the 

 sandstone of the dike is Tertiary, or to speak more strictly, Oligo- 

 cene, and therefore considerably newer. The sand must then have 

 been intruded into the clay not from below but from above. Now 

 let us consider what were the circumstances of the formation of 

 the dikes. 



The formation of the fissures long before their infilling and the 

 slow accumulation of sands in them, such as may have occurred in 

 the case of the fissures in the Carboniferous Limestone of the 

 Mendips, cannot be considered as probable, the clay being soft and 

 the sandstone homogeneous, and the latter having none of the 

 characters of a slowly accumulated deposit. We must conclude, 

 therefore, that the fissure was opened and quickly filled with the 

 sand which was on the spot ready to fill it. 



We can represent to ourselves the march of events in the region 

 of Alatyr before and after the formation of these dikes somewhat as 

 follows. 



The Lower Cretaceous sea deposits here a thick mass of clays 

 interstratified with beds of glauconitic sand. The existence of 

 Gault in the neighbourhood shows that these conditions were con- 

 tinued also into the Gault period. We may also suppose, with all 

 probability, that during part of the Upper Cretaceous time this 

 was a littoral part of the sea, because the northern boundary of 

 the Upper Cretaceous beds does not pass far from here to the 

 south. After Upper Cretaceous times, the region becomes dry 

 land, and the Upper Cretaceous and Gault deposits are exposed to 

 denudation. A new transgression of the sea begins in the Lower 

 Oligocene time, during which the Oligocene sea covers the Lower 

 Cretaceous clays and lays down its sandy sediments on their surface. 

 While this Oligocene sand was still not too thick, an earthquake 

 occurs and the seismic fissures tear the floor of the sea, penetrating 

 into the Neocomian clay ; and the Oligocene sand, containing many 

 shells, quickly fills up the fissures. After a time the level of the 

 sea falls, the dry land reappears in the region, the process of 

 denudation recommences, and the Tertiary strata disappear almost 

 entirely from the country. In Quaternary times a marginal part 

 of the great ice-sheet passes through the counti'y, and the old 

 alluvial sands are deposited on the lower parts, and we should never 

 have known that the Oligocene sea once covered this region, if 

 a little sample of its sediment had not escaped destruction by 

 being concealed deep in the fissures of the sea floor. 



If this explanation be correct, we have here an interesting in- 

 stance of the means by which nature notes the events of her history. 

 The earthquake breaks for a moment the regular march of events, 

 and the sea with its sandy floor becomes for the occasion a seismo- 

 graph, and notes this event and the time at which it took place. 



