MARR : YORKSHIRE AND SCANDINAVIA. 147 



Europe was largely occupied by a great ocean tract, the deposits 

 formed therein varied considerably in different regions. These 

 Yorkshire deposits are of interest as forming to some extent a 

 connecting link between the slate-rocks of the Lake district and the 

 ancient silts of Scandinavia. The oldest rocks visible are the green 

 slates of Ingleton, no doubt largely derived from the destruction of 

 some volcanic tract such as occurred about the time of their formation 

 in the adjoining Lake country area. Resting upon them are some 

 calcareous shales, forming the top of the Ordovician system, and 

 undoubtedly equivalent to the more calcareous strata known further 

 west as the Coniston Limestone, but having affinity also with the 

 more clayey Trinudeus shales of Sweden. It is interesting to find 

 an old acid lava at Wharfe Mill Dam near Austwick, for great 

 masses of such lavas were poured out in the region of the Lakes 

 and in North Wales at this time, and the equivalent shales of the 

 island of Bornholm contain some ashy bands. The characteristic 

 Triniuiens of these shales in Sweden occurs in abundance at Norber 

 near Settle, where it is accompanied by a beautiful and rare trilobite 

 of the genus Dindymene, which is also found in Sweden. 



Of recent years, the study of the remarkable sea-pens known as 

 graptolites has led to their utilisation as a means of correlation of 

 these early sediments and we find at Norber the form Dicellograptus 

 anceps which occurs in beds of this age in Sweden. 



The Silurian rocks of Yorkshire are of Llandovery, Wenlock and 

 Ludlow ages. To the former age is assignable the Pliaeops elegatis 

 limestone, containing a trilobite characteristic of the equivalent beds 

 in Norway where it was first described, whilst, in the Sedbergh area, 

 we find a group of graptolitic shales of this age with the genera 

 Monograptiis, Rastrites, Diniorphograptus and other forms marking 

 this horizon over a large part of Europe. 



To the Wenlock beds belong the flags of the Wharfe Valley, 

 containing Monograptus pn'odon, and Retiolites geinitzianus also 

 found very widely distributed. 



Above these are grits, to some subordinate shales of which the 

 remarkable Moughton whetstones are probably referable. They 

 contain Monograptus nilssoni and M. dubius found on the same 

 horizon in Scandinavia and marking the base of the Ludlow series. 

 They are succeeded by the flags of the great quarries of Ribblesdale 

 with Monograptus colonus, M. rxmeri and M. bohemicus, above 

 which are some grits also referable to the Lower Ludlow, and 

 forming the highest Silurian rocks of this area, though still higher 

 beds, the Bannisdale slates occur near Sedbergh and equivalents of 

 the Upper Ludlow are found immediately west of the Lune. 



May 1890. 



