Bevieivs — The Survei/ Memoir on the Scottish Uplands. 515 



Everywhere, as in the Moffat country, the massive arenace^ous 

 group of the Gala-Tarannon succeeds at once to the Moffat Series 

 throughout the whole of the Central Belt. But it is evident that 

 the assumption of the arenaceous facies by successive zones of the 

 Birkhill division as we pass from the Moffat country northward 

 renders it difficult, if not impossible, to fix in every instance the 

 horizon where the Birkhill strata end, and the Gala beds begin. 

 This monotony of lithological facies is especially tantalizing along 

 the northern edge of the Central Belt, where the arenaceous facies 

 has descended far into the heart of the Hartfell itself. The northern 

 boundary of the Central Belt is presumably defined as tlie outcrop 

 of the line which divides the local Hartfell from the local Birkbill — 

 i.e., it is the line of division between the Ordovician and Silurian 

 of tbe Uplands. But the lithological transition between the strata 

 of the two systems is hero almost as gradual as that between the 

 Cambrian and Ordovician of other countries, and the line laid down 

 upon the map by the officers of the Survey is therefore admittedly 

 generalized and provisional. 



A few observations may here be made with reference to the 

 names of the graptolite species cited in the abundant fossil lists 

 scattered through the work. These lists may each be regarded from 

 two aspects, the one stratigraphical and the other palaeontological. 

 Regarded from the stratigraphical aspect the lists subserve well the 

 purposes for which they have been drawn up, namely, those of 

 correlating the beds which contain them with the tj'pe zones of 

 Moffat and Girvan. The general association of forms is usually 

 sufficient for this pui'pose, and the exact identification in situ of 

 every species as at present defined by the graptolithologist is from 

 this point of view a matter of no great moment. But regarded 

 from the palajontological aspect the matter is very different. The 

 names of many of the forms given in the lists must be read as 

 provisional and suggestive only, namely, as those of species which 

 are called to mind by the form detected at the locality : for example, 

 the forms united under Monogrnptus Hisingeri may in reality belong 

 to several distinct species ; the same is the case with M. tenuis, 

 M. priodnn, M. lobiferns, M. tiorriculatus, Dimorphograptus Swanstoni, 

 Dicranograptiis ramosus, and others. 



Here perhaps we may also call attention to a practice of paleeonto- 

 logists, admirable enough in its way, but which, when carried out to 

 the extent displayed in the present work, borders very closely on 

 the ridiculous. We refer to the habit of appending the name of the 

 founder of each species in every instance where that species is 

 cited. For example, such titles as Diplograptus folinceus (Murch.), 

 Dicranograptiis rnmosns (Hall), Monograptiis gregarius (Lapw.), 

 occur hundreds of times witliin the cover of this volume. Now 

 tliere can be no question that it is advisable for the sake of 

 scientific accui-acy that the reader should be told what special form 

 the writer regards as the type of the species identified ; but having 

 appended the nnme of the founder to that of the species once iu 

 his general table of species and once where it is first mentioned 



