14-2 Geological Society. Prof. Sedgwick on the 



with the great development of red sandstones in many parts of the 

 true carboniferous series of Scotland, he concludes that the highest 

 stratified beds of Arran do not represent the new red sandstone, but 

 (more probably) a portion of the carboniferous group. To the upper 

 conglomerates of Arran there is however no counterpart in England ; 

 and the exact place of the red beds which overlie them is still left in 

 some doubt ; but these upper conglomerates may perhaps be compared 

 with some great trappean conglomerates which are subordinate to 

 the Scotch coal-fields. 



Carboniferous series. — The author briefly notices the changes in 

 this series during its range from the northern counties of England 

 into the basin of the Tweed, where a coal-field occurs developed after 

 the Scotch type, and far below the great coal-field of Newcastle. He 

 then discusses shortly the carboniferous deposits of Scotland, which 

 are divided as follows, in descending order : — 



1 . The rich coal deposits with numerous beds of coal ; in their 

 subordinate beds of shale, ironstone, fire-clay, and fossils, presenting 

 the closest analogies to the great English coal-fields. Their exact 

 place in a general scale cannot however be determined, as they offer 

 no passages, like those above noticed, into any higher formation. 



2. A great group with many thin bands of carboniferous limestone, 

 alternating with sandstone and shale; and generally with well-defined 

 thick beds of limestone at the top of the group, so as to form the base 

 of the most productive coal-fields. This group also contains beds of 

 coal, but generally of inferior quality. The alternating sandstones 

 are not unusually of a red colour. 



3. Beds of red sandstone, shale, &c. — They undergo many modifica- 

 tions of structure and colour, and are in some places of great thick- 

 ness. In some of their higher portions they contain coal-plants, 

 and even thin bands of coal; but they pass downwards by grada- 

 tions the most insensible, and blend themselves with the old red 

 sandstone. Examples of such passages are found on the north side 

 of St. Abb's Head, on the north shores of the Solway Firth, and on 

 the coast of Ayrshire. 



The Dumfries- shire carboniferous groups are developed after the 

 Scotch type above described ; which is the more remarkable, as the 

 groups on the south side of the Firth conform to the English type. 

 Near Whitehaven there is no passage from the carboniferous lime- 

 stone to the old red sandstone ; and the thickest beds of limestone 

 are at the bottom, and not (as in Scotland) at the top of the calca- 

 reous series. 



The author then notices the geological map of Scotland, and 

 states that Dr. M'Culloch has not merely introduced much con- 

 fusion by giving the mountain limestone series and the old red 

 sandstone a common colour ; but that he has committed a great 

 error in principle, by confounding, along a considerable part of the 

 country bordering on the north shores of the Solway Firth, the new 

 with the old red sandstone. 



Old Red Sandstone. — The author, after briefly noticing the ex- 

 traordinary irregularity in the development of this formation in the 



