355 



III. PETROLOGY. 



The uppermost stratum bounding the Middle Lias, which in 

 fact crowns this important division of the Lias formation, is 

 the Spinatus sands. These sands, as a whole, form the Spinatus 

 Zone of the Middle Lias. The beds of this zonal division in 

 the Northern part of Gloucestershire,, attain a thickness 

 varying from 6 ft. 6 in. to 6 ft. 8 in. at Churchdov^ an outlier 

 of the Cotteswolds ; and in its general character as compared 

 with rocks in the same relative position in other parts of Europe, 

 constitutes a distinct subdivision of the Middle Lias, having its 

 peculiar character, whether regarded as to its fossil contents, or 

 the nature of its petrology. The beds consist of buff-coloured 

 incohering or slightly compacted sandstone of fine grain and 

 marly character, sometimes inclining to a drab tone, more often 

 to a dirty yellow hue, such as artists term a broken yellow, and 

 it is singular that wherever these sandstones occur homotaxially, 

 throughout IST. West Germany, they are invariably described as 

 yellow sandstones. The Churchdown Spinatus sandstone contains 

 a small but varying proportion of marl desseminated throughout 

 the mass, which is a fine grained sandstone; and which, as 

 regards hardness, is nowhere sufficiently compacted to be of 

 any service for road metal or building stone. Hence probably 

 the neglect of the material of this division by geologists — for it 

 is never exposed in stacks like the Marlstone on which it rests. 

 The quarries at Churchdown, and generally in the Cotteswolds, 

 are opened for the sole purpose of getting road metal from the 

 rock bed of the Margaritatus zone, and in order to reach this 

 bed, the sandstone of the Spinatus capping must first be 

 removed. The blocks of sandstone removed from the quarry 

 are tilted on one side to be out of the way of the quarrymen, 

 and there the spoil bank can be easily examined, if taken in 

 time, but there must be no delay, certainly not a couple of 

 winters between, as under the influence of rain and frost, they 

 soon present to the eye nothing but a muddy shapeless 

 sand-heap, at least, the softer portions of them, for some of the 

 harder blocks withstanding such agencies longer, present on 



