POPULAR GEOLOGT. 21 



have been worn away to a sufHcient extent the whole thickness of the 

 rocks above falls down leaving a perpendicular cliff. These cliffs form an 

 interesting feature in most of our deep valleys. But very often the face 

 of these rocks is hid by a mass of fallen debris, and in this case they 

 will slope down into the valley with an angle of inclination varying with the 

 depth and width of the valley. Any person who has watched the progress 

 of the new line to Ovenden, will have seen what a mass of stone and 

 rubbish had to be removed before they came to the face of the solid rocks, 

 all along the edge of the valley on each side of North Bridge and Wood- 

 side Bottom. Those Avho study the subject cannot fail to arrive at the 

 conclusion, that tlie whole of this plain was at one time continuous, and 

 instead of being as at present divided by these two valleys (the 

 Calder and Hebble valleys) it was one great bed of sandstone rock. Hard 

 and comparatively indestructible as these grit-rocks are, the weather-worn 

 crags of Shroggs, Skircoat, Norland, &c., shew that even they undergo 

 great changes. The sand and quartz of pebbles, and wasted rock tell 

 of the desti'uction going on, imperceptibly it may be to us, but still in 

 the lapse of ages Avorking a permanent change. And when we come to 

 think of the vast period that has elapsed as Professor Eamsay says, since 

 these rocks were formed, and that all the newer formations have been 

 formed out of the waste of the older ones, Ave cannot Avonder at the extent 

 of the denudation. The Avhole thickness of the millstone-grit series in 

 this neighbourhood is according to Professor Phillips, about 900 feet. 



"millstone grit fossils." The fossils foimd in these shales and 

 limestone bauds are chiefly marine shells of the genera Lingula, Modiola, 

 Pecten, Goniatite, Orthoceras, Veims, &c. They occur very &paringly, and 

 on account of the perishable nature of the shales, they are rarely found 

 perfect.* In certain layers mostly composed of crushed Goniatites I have 

 found the impressions of narroAV plants similar to the" Calamite but neither 

 j ointed nor fluted and probably they are like the shells, of marine origin. The 

 sandstone rock contains fragments of fossil plants for they are, very rarely 

 found perfect, belonging to the genera Sigillaria, Stigmaria, Sternbergia, 

 Lepidodendra Calamites, &c., all of Avhich occur more abundantly in the 

 coal beds above. They are A'ery thinlj' strcAvn in the grit-rocks and seem 



'Some A-ery good fossils haA*e been found in the layer of limestone nodules A\'hich 

 crops out in Criniswoith Dean and Hebden valley, but these 6tiata are supposed 

 to belong to the Yoredale rocks bcloAv the Millstone-grit. 



