220 Geological Society : — Anniversary of 1839. 



than it at first appeared to be. Of this progress of things exam- 

 ples are too obvious and too recent to require to be pointed out. 



The labors of Professor Sedgwick refer to the " Cambrian Sys- 

 tem," which lies beneath the Silurian System, occupying much 

 of North Wales, Cumberland, and a great part of Scotland ; while 

 the Silurian System spreads over a great part of South Wales and 

 the adjoining English counties. The classification of the rocks 

 of this portion of our island to which Professor Sedgwick has 

 been led, though laid before you only at a recent meeting, is the 

 fruit of the vigorous and obstinate struggles of many years, to 

 mould into system a portion of geology which appeared almost too 

 refractory for the philosopher's hands ; and which Professor Sedg- 

 wick grappled with the more resolutely, in proportion as others 

 shrank away from the task perplexed and wearied. I need not 

 attempt any detailed view of his system : his First Class of Pri- 

 mary Stratified Rocks occupies the Highlands of Scotland and the 

 Hebrides, and appears in Anglesea and Caernarvonshire ; the 

 crystalline slates Skiddaw Forest, and the Upper Skiddaw slate 

 series come next. Above these is his Second Class, or Cambrian 

 and Silurian. The Cambrian is divided into lower and Upper 

 Cambrian, of which the former includes all the Welsh series un- 

 der the Bala limestone ; the two great groups of green roofing 

 slate and porphyry on the north and south sides of the mineral 

 axis of the Cambrian mountains (of which groups the position 

 had previously been misunderstood), and parts of Cornwall 

 and South Devon. The Upper Cambrian System contains a 

 large part of the Lammermuir chain ; a part of the Cambrian 

 hills, commencing with the calcareous slates of Coniston and 

 Windermere ; the system of the Berwyns and South Wales ; 

 all the North Devon, and a part of the South Devon and Cor- 

 nish series. Ascending thus through a series of formations dis- 

 tinguished and reduced to order by the indefatigable exertions 

 and wide views of Professor Sedgwick, we arrive at the Silurian 

 system ; and here we must seek our subdivisions from the rich 

 results of the labors of Mr. Murchison. These subdivisions were 

 published in the summer of 1833. Like the Cambrian, the Silu- 

 rian is divided into a Lower and an Upper System, the former 

 including the Llahdeilo flags and the Caradoc sandstones ; the 

 Upper Silurian Rocks being the Wenlock shale and limestone, the 

 Lower Ludlow, the Aymestry limestone, and the Upper Ludlow, 



