90 Corresjjondence — Messrs. Blake and Hudleston. 



subsidence having continued to the level of the present raised beaches, 

 reelevation took place, producing greater cold and more extreme 

 seasons, and culminating in the production of continental conditions, 

 permitting the southward migration of a temperate fauna, and the 

 advent of one requiring greater cold. During this period the gravels 

 connected with the formation of the present valley system, the raised 

 beaches, and the "Head" were produced, and, doubtfully, part of the 

 cave-earth and the granular stalagmite of Kent's Cavern, and the clay 

 of Petrockstow and Roundswell. In the last subperiod the author 

 considered that a subsidence took place during which most of the 

 valleys were excavated to their present depth, and forest growth took 

 place upon the old marine plain; the forests were then gradually cir- 

 cumscribed by the encroaching sea and diminishing rainfall, which 

 also led to changes in the streams, and finally the sea entombed the 

 forests and swamps on the coasts, and produced the present cliff-line. 

 The results of this period are the submarine forests, most of the 

 river- valley gravels, and alluvial tracts bordering the present river- 

 courses. 



ooI^I^:E]s:F'OI^^ID:BI^^o:E]. 



THE CORAL RAG OF UPWARE. 



Sir, — In the October Number of the Geological Magazine 

 Professor Bonney points out certain facts observed originally by Mr. 

 Henry Keeping — but subsequentlj' confirmed by himself — which are, 

 he considers, incompatible with " the ■presumed section" near Upware 

 given in our paper " On the Corallian Eocks of England," Quart. 

 Journ. Geol. Soc, voL xxxiii. p. 315. 



Our object in attempting the section referred to was to show how 

 the palasontologically higher beds of the south pit could overlie those 

 of the north pit — though they dip towards them ; and that they may 

 do so, unless we call in the aid of a fault, the existence of a synclinal 

 is the most natural supposition. Beyond this, the stratigraphy was 

 irrelevant to our paper — and we readily admit that the unconformity 

 between the Corallian rocks and the newer strata might have been 

 more clearly shown. We would merely remark that Mr. Keeping's 

 section, being at right angles to ours, can throw no light on its 

 correctness. 



The true reading of the sequence of the Corallian rocks — which, 

 as indicated in column ix. of our table of comparative sections, is 

 not seen — rests entirely on palseontological evidence, and this, 

 though he admits that we may be right " in assigning to the rock of 

 the northern pit a lower horizon than that of the southern," Pro- 

 fessor Bonney considers not to be strong. Here then is the only point 

 really at issue between us. We can only say that the two urchins 

 which by their abundance characterize the northern pit, are " species 

 usually indicative of a low position " (see our memoir, p. 367), and 

 their occurrence on or above the horizon of a Bag fauna would be 

 another of those surprises with which we will admit the Corallian 

 series abounds. 



