308 ANNUAL OF SCIENTIFIC DISCOVERY. 



" In the mean time, reverting to the region of "Wales and the adjacent 

 English counties, we can appeal to the admeasurements of the Govern- 

 ment surveyors. In Shropshire, the uiifossiliferous bottom rocks (the 

 Cambrian of the Survey) are said to have the thickness of 26,000 feet, or 

 about three times that of the same strata in North Wales ; whilst my 

 original Lower Silurian strata of Shropshire to the west exhibit a width 

 of 14,000. On the other hand, in the region between the Menai Straits 

 and the Berwyn Mountains, where the bottom rocks are so much less co- 

 pious than in Shropshire, the fosiliferous Lower Silurian, from the base of 

 the Lingula flags to the top of the Llandeilo formation, (including the 

 stratified igneous rocks,) swell out to about 19,000 feet, and the Caradoc 

 sandstone has a thickness of from 4,000 to 5,000 feet. Taking the greatest 

 dimensions, we are, therefore, presented with the prodigious measurement 

 of about 50,000 feet of sedimentary strata, in the lower half of which no 

 fossils have been found, the upper part bearing a group of fossils. Al- 

 though of such vast volume in parts of the region described, it must be 

 observed that the Lower Silurian rocks of other tracts, though precisely of 

 the same age, as proved by their embedded organic remains, are often 

 comparatively of very small dimensions. 



" Though more replete with fossils than the inferior group, the Upper 

 Silurian rocks attain nowhere a greater thickness than from 5,000 to 6,000 

 feet, the Ludlow rocks being for the most part more developed than the 

 Werilock formation. In this way the whole of the fossiliferous Silurians 

 of England and Wales, measured from the Lingula beds to the Ludlow 

 rocks inclusive, have the enormous maximum dimensions of about 30,000 

 feet ; and if we add the conformable underlying sedimentary masses of 

 pretty similar mineral aspect, but in which no fossils have been found, we 

 have before us a pile of subaqueous deposits reaching to the stupendous 

 thickness of 56,000 feet, or upwards of ten miles ! " 



In reference to the supposition that the Lower Silurian rocks present 

 the earliest zone of animal life, Sir 11. Murchison says : 



" This is the important fact to which attention is first directed ; for in 

 such instances the geologist appeals to the book of Nature, where its 

 leaves have undergone no great alteration. He sees before him an enor- 

 mous pile or series of early subaqeous sediment originally composed of 

 mud, sand, or pebbles, the successive bottoms of a former sea, all of 

 which have been derived from preexisting rocks ; and in these lower 

 beds, even where they are little altered, he can detect no remains of former 

 creatures. But lying upon them, and therefore evolved after, other strata 

 succeed, in which some lew relics of a primeval ocean are discernible, 

 and these again are eA r ery where succeeded by newer deposits in which 

 many fossils occur. In this way evidences have been fairly obtained to 

 show that the sediments which underlie the strata containing the lowest 

 fossil remains constitute, in all countries which have been examined, the 

 natural base or bottom rocks of the deposits termed Silurian." 



