100 REPORT—1840, 
of soft clay of the form of pebbles, such as are still formed every day 
on the shores of the Mersey, are found imbedded in the sandstone, and 
thin seams of clay are interposed between the sandstone strata. The 
footsteps are found on turning up the broken pieces of one of these 
strata; for they occur on its under surface, and are in fact casts, not 
original impressions. This under surface rests upon a seam of fine clay 
about one quarter of an inch in thickness. Without the intervention 
of the clay which has been deposited between the beds of sand, it is 
manifest that neither ripple-marks nor footsteps would have been pre- 
served. But it appears, that soon after the deposit of a thin bed of 
clay upon the soft sand, amphibious quadrupeds, probably allied to cro- 
codiles, monitors, or other saurians, traversed the shore of the then 
existing river, and left their footsteps impressed upon the clay. The 
water having again overflowed the shore, deposited a bed of sand, fill- 
ing the impressions of the animals’ feet, and consequently, on the indu- 
ration of the sand and its conversion into stone, producing those casts 
which are now discovered. 
“Tt is almost unnecessary to remark, that the Liverpool sandstone 
does not differ in its geological relations from that of Stourton, both 
belonging to the new red sandstone formation.” 
On the great development of the Upper Silurian Formation in the Vale of 
Llangollen, North Wales, and on a Plateau of Igneous Rocks on the 
East Flank of the Berwyn range. By J. E. Bowman, F.G.S. 
In the course of a recent examination of the boundary line between 
the Silurian and Cambrian rocks in North Wales, undertaken at the 
suggestion of Mr. Murchison, the author came in contact with the for- 
mations that form the subject of his paper, and which do not appear 
on the latest geological maps. He showed, by the aid of two enlarged 
sections, taken on the spot and rendered more complete by data libe- 
rally furnished by Colonel Colby, of the Ordnance Office, that the 
shales and slates which compose the hills for some miles north and 
south of the vale of Llangollen, and extend westward nearly to Cor- 
wen, belong to the Upper Silurian formation. ‘These rocks have here 
completely lost the character of the soft brown “mudstones” of Shrop- 
shire and Montgomeryshire, and in many places resemble the Cambrian 
series, slates and flags with perfect cleavage being extensively quar- 
ried at Glyn, Oirnant, &c. Their true geological position was satis- 
factorily proved, by their being seen rising from under the Upper 
Ludlow rock of Castell Dinas Bran, in which Mr. Bowman found 
Terebratula Navicula, Cypricardia, &¢c., and by their lowest beds re- 
posing on the fossiliferous Lower Silurian rock of Cyrn y Brain, These 
proofs were confirmed by the no less conclusive evidence of fossils, 
Orthocerata, Graptolithus Ludensis, and Cardiola interrupta being 
found in some of the quarries. 
Unlike the soft and uniform equivalents of these rocks, made fami- 
liar to geologists by the labours of Mr. Murchison, they here consist 
of three principal groups, which insensibly pass into each other, and 
