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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 Sedgwick grappled with the more reso- 
lutely, 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 Primary Stratified Rocks occupies the Highlands 
of Scotland and the Hebrides, and appears in Anglesea and Caernar- 
vonshire ; the crystalline slates of Skiddaw Forest, and the Upper 
Skiddaw slate series come next. Above these is his Second Class, 
or Cambrian and Silurian System. The Cambrian is divided into 
Lower and Upper Cambrian, of which the former includes all the 
Welsh series under 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 Cumbrian 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 Cumbrian 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 Cornish series. Ascending thus through a series 
of formations distinguished 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 labours of Mr. Murchison. These subdivisions 
were published in the summer of 1833. Like the Cambrian, the Si- 
lurian is divided into a Lower and an Upper*System, the former in- 
cluding the Llandeilo 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, which 
finally conducts us to the Tilestones or bottom beds of the Old Red 
Sandstone. 
That these various series of Cambrian and Silurian rocks are 
really superposed on one another; that they are justly separated into 
