no Sheppard : The Making of East Yorkshire. 



section of the earth's crust, and that the earth's crust itself, 

 some 20 miles in thickness, is but a moiety of the world 

 proper, we can form some vague idea of the length of geological 

 time. 



From some cause or other the Liassic sea became elevated, 

 the water and its inhabitants found a resting place elsewhere. 

 What was once an ocean floor became for the time being dry 

 land, which eventually again finds its level beneath the sea, and 

 upon the Liassic rocks is a great series of limestone and shales 

 of newer date belonging to the Oolitic system. 



These Oolitic beds have been classified as under : — ' Dogger, 

 Lower Estuarine Series with ' Eller Beck Bed,' Millepore Bed, 

 Middle Estuarine Series, Scarborough or Grey Limestone, Upper 

 Estuarine Series, Cornbrash, Kellaways Rock, Oxford Clay, 

 Lower Calcareous Grit, Greystone or Passage Beds, Lower 

 Limestone and Coral Rag, Middle Calcareous Grit, Upper 

 Limestone and Coral Rag, Upper Calcareous Grit,' and these 

 divisions are further divided according to their characteristics. 

 To examine each of these in detail is an undertaking which 

 cannot now be embarked upon ; it is perhaps sufficient to state 

 that they comprise a series of rocks altogether measuring 

 some thousands of feet in thickness, of great variety, and 

 indicate a great number of changes on the earth's crust during 

 their formation. Take, for example, some of the rocks : the 

 Millepore Bed (so called from a minute coral occurring therein 

 which is perforated with small holes or pores) is a characteristic 

 roestone or Oolitic rock. If a specimen, such as might be 

 obtained at Hotham, or Brough, or on the cliffs near Scar- 

 borough, be carefully examined, it will be found to consist of 

 minute globules of lime, cemented together very much after the 

 manner of the roe of a fish. It is from this character, which is 

 also found in other beds of the Oolitic system, that this par- 

 ticular series derives its name, from the Greek word 00?/ — an 

 egg ; and it is perhaps only natural that early philosophers 

 assumed that these entire rocks, extending for miles, and of 

 great thickness, really represented fossil fish-roe ! Modern 

 science has changed all that. Examined under a microscope 

 each globule is found to consist of a number of concentric layers 

 of lime, surrounding a small nucleus — usually a very small sand 

 grain, a shell of a foraminiferon, or some other similar object. 

 These small particles, moving to and fro in water super- 

 saturated with lime, have become coated layer after layer with 

 the substance in a similar manner to the familiar instance of 



Naturalist, 



