W. M. Hatchings — The Origin of some Slates. 265 



much still remains to be done before we are able, in a satisfactory- 

 manner, to read in the slates, shales, sandstones, etc., the record of 

 their origin and subsequent development ; and so, as Mr. Sorby says, 

 to "as it were, sometimes trace back the genealogy of our globe a 

 generation or more earlier than by other means." 



The following notes, resulting from considerable study of some 

 of the materials in question, have only a limited bearing on a limited 

 portion of this very wide subject, but are offered in the hope that 

 they may not be wholly wanting in value as a contribution towards 

 explaining some of the questions involved. 



During the examination of a series of sections of slates (roofing- 

 slates and closely similar material from Wales and Cornwall), two or 

 three special points of interest arose which led me to wish to study in 

 detail some more recent deposits, which might show less advanced 

 stages of the chemical and morphological changes which have taken 

 place in the original sediments. At the same time I specially wished 

 to have deposits as to which one could be quite sure that they were 

 derived from the waste of granite areas. Materials answering these 

 requirements are to hand in the Carboniferous formation, and espe- 

 cially in the Coal-measures, the sandstones, shales, etc., of which 

 are, I think, usually considered to have been derived from granites, 

 and this has certainly been the case with some of them that I have 

 worked upon. 



Some of the observations made appear to have sufficient bearing 

 on the eventual development of certain slates to warrant a rather 

 detailed account of them. 



I will select for description the materials of a bed exposed in the 

 cliffs near the village of Seaton, a few miles north of Newcastle-on- 

 Tyne. This bed, several feet thick, is composed mainly of indurated 

 clay of various degrees of fineness. The finest does not show to eye 

 or pocket-lens a flake of mica or a grain of any sort of sand, and 

 yields when ground with water a clay of the highest degree of 

 smoothness and plasticity. Bands of this alternate with others in 

 which more or less mica is seen with the naked eye, and which, 

 while still fully plastic with water, contain a good deal of gritty 

 sand. These again pass into still coarser layers, while here and 

 there are bands, some inches thick, of fine-grained, laminated, soft 

 micaceous sandstone. There are also, at places, very thin bands of 

 clay-ironstone. Lamination is not so well marked in the finest clay 

 as in the coarser and harder bands, where it is highly developed ; 

 such bands verging in nature towards soft shales. 



The greater part of the bed in question is really a more or less 

 coarse-grained " fire-clay," similar in all respects to the fire-clays 

 worked on a large scale in the district, differing only in the mode of 

 occurrence, the regular beds, with the seams of coal, being mostly 

 more or less unstratified and irregular. 



Above the bed just described is one of several feet of micaceous 

 sandstone, followed by a series of several feet of clays, soft shales, 

 and sandstones, with a very thin seam of coal ; and finall}' a con- 

 siderable thickness of hard compact sandstone. The whole has 



