428 STRATIGRAPHICAL GEOLOGY 



On the Yorkshire coast the whole group is represented by shales 

 and sandstones of estuarine origin, capped by a thin band of 

 Cornbrash. 



In Gristhorpe Bay this Upper Estuarine Series is 120 feet thick, 

 consisting of marine sandstones in the lower part and shales with 

 thin sandstones above. Farther north they are over 200 feet 

 thick. A few ferns are the only fossils. 



The Cornbrash is very thin, only 5 or 6 feet, but has the usual 

 characters, being a grey rubbly ironshot limestone full of the 

 ordinary fossils, among which are Macrocephalites Herveyi, Pseudo- 

 monotis echinata, Lima rigidula, and Waldheimia lagenalis. 



D. THE MIDDLE JURASSIC IN SCOTLAND 



1. West Coast 



" Bocks of this age," says Professor Judd, 16 " must have origin- 

 ally had a very wide distribution, for traces of them are found at 

 various points from the Shiant Isles in the north to Ardnamurchan 

 in the south. The best exposures of their strata, however, are those 

 which occur in the islands of Skye and Raasay" (see Fig. 132). 



Here the Inferior Oolite consists of the following beds : 



Feet. 



Beds of white sandstone with thin shaly bands containing remains 



of ferns and cycads ........ 60 



Beds of sandstone and shale, the former passing into shelly lime- 

 stones, Steph. Hiimphriesianum, Belemnites giganteus . . 160 



Sandy micaceous shales alternating with calciferous sandstones, 

 Ludwigia Murchisonoe, Harpoceras corrugates, Belemnites 

 giganteus, Lucina Wrightii, etc 120 



340 



These beds are succeeded by a great thickness of strata belonging 

 to the Bathonian Group. At the base are marine limestones 

 almost wholly made up of comminuted shells, but containing 

 perfect Ostrea Sowerbyi, Waldheimia lagenalis, etc. They probably 

 represent the zone of Parkinsonia Parkinsoni and are 45 feet thick. 

 Above them are estuarine sandstones and shales fully 500 feet thick 

 but not well exposed. 



Farther south, however, in the islands of Eigg and Muck this 

 estuarine group is still thicker and is accessible, the following 

 succession being seen : 



A. The lowest beds are fine conglomerates and shelly limestones 

 full of freshwater shells, but containing also remains of Plesiosaurus, 

 turtles, and other reptiles. Above these are black shales and 

 limestones abounding in Cyprids, fish remains, and shells of Cyrena, 



