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■when in continnous layers, it is easy to see that it is only by the union of 

 a great number of nodules that they take the form of a continuous plate. 

 These nodules appear to be formed by the hardening of the shales around, 

 a central organic object. The hardening and impregnating material being 

 sometimes carbonate of iron, that produces clay iron stone nodules, some- 

 times carbonate of calcium, sometimes silica, and sometimes sulphide of 

 iron, and these are generally associated together ; the preponderance of 

 one or other of these substances giving the nodule its characteristic name. 

 The objects contained in these nodules are numerous : sometimes it is a leaf, 

 or fern frond, or terminal bud, in which case the actual tissue is present, 

 and the very finest lines visible. Sometimes it is a twig, stem, root, fruit, 

 or may be a shell, in which case it may have been permeated with carbonate 

 of iron, and carbonate of lime, or iron may have replaced the lime, but it 

 often shows the finest lineaments, and also every cell of the structure. At 

 other times we find organic objects scattered through the mass of the 

 nodule. It is important to direct attention to the condition of these 

 entombed objects. When woody matter is present, it is often crushed, and 

 shows that it has been subjected to violence. It has been withered or dried, 

 and has become dead wood, often bored by insects, and it almost invariably 

 shows the rootlets, running through its mass, of other plants which have 

 grown around and upon it after its fall. These facts go to show the time 

 at which these substances became petrified, which must have been not long 

 after they were laid down, and certainly the earlier portions of the- 

 concretions were formed before the change of woody matter into coal 

 commenced, and before the coal measures became faulted, and the strata 

 were subjected to the intense pressure which came into action when the 

 coal measures were upheaved, for we find that the nodules have moved andl 

 elided in the shales and coals ; for all of them in the neighbourhood of a 

 fault are slickensided with their motion, and often the shales are seen to 

 laminate concentrically with the nodule, showing that they have been 

 laterally squeezed into another place. Mr. Holgate described the mode of 

 agglomeration of iron stone nodules and coal balls, and stated that he 

 believed their formation might be attributed to the presence of a water 

 containing iron, lime, silica, and sulphur in a goluble state ; that this water 

 had flowed over this organic matter, probably after it had received a 

 covering of mud, and had permeated through the mud, depositing the 

 chemical matter in and around the organic substances. The action haa 

 probably gone on ever since, and is giong on now, for we find that where- 

 ever there are layers of ii-on stone nodules, there is a slow passage of water 

 through that horizon. For the origin of these chemicals we had not far to 

 look, when we considered that volcanoes were in existence at Edinburgh, 

 Keswick, and Charnley Forest, vomiting these substances, and that the 

 movement of the water most probably was from one or other of these 

 places. Mr. Holgate then took up the question of flints, and showed that 

 their formation must have been of a similar character. They are of 

 nodular form, the objects embedded in them are almost invariably damaged 



