152 



THE GEOLOGIST. 



Farringdon Gravels. — Sir, — In his paper on the Farringdon Sponge- 

 gravel, in the January number of the ' Geologist,' Mr. Meyer says that 

 " it is no new idea to compare the Farringdon deposits to the sands and 

 gravel of Devizes " (Lower Green sand). I have always thought that 

 nearly all geologists classed the Farringdon beds with that formation. Mr. 

 Hull has mapped and described them as such in sheet 13 of the Geological 

 Survey Map, and at page 13 of the Memoir, illustrating that sheet with 

 regard to the order of the beds, Mr. Hull says, " The beds at Farringdon 

 are divisible into two groups ; the lower being the fossiliferous gravel and 

 conglomerate, the upper, clays and sands, with iron-bands," which agrees 

 with Mr. Meyer's conclusion, that the Sponge-gravel is the oldest of these 

 deposits. I am yours, etc., W. W. 



Errata — Mr. Whittaker's Lecture. — Page 58, line 8, after "until" 

 insert " in ; " page 58, line 9 from bottom, after " altogether " insert " of ;" 

 page 58, line 5, for " supposed " read " supposes ; " page 59, line 16, after 

 " Cray " insert " the ; " page 59, line 34, before " London " insert " the ; " 

 page 60, line 3, for " abundance Cyrena, Cerithium, and Melanin " read 

 " abundance (Cyrena, Cerithium, and Melania) ; " page 61, line 13, erase 

 the bracket after " common," and insert it after "rays" in the following 

 line. 



Cause of the Geysers. — In Mr. Reed's paper " On a New Theory 

 of the Generation of Steam," before the Liverpool Philosophical Society 

 (1862-3), he gives the following summary of the principles laid down by 

 Mr. Williams, the originator of the theory : — 



" 1st. Water, or its atoms, can neither be heated nor expanded and still retain the 

 character of liquidity. 



" 2nd. The prevailing theories as regards ebullition are altogether erroneous. 



" 3rd. The so-called boiling-point, as regards temperature, is merely that point ai 

 which the water is charged with vapour to saturation, under the true Daltonian theory, 

 the water acting the part of a mere vacuum or medium. 



" 4th. We have strong grounds for believing that there is no difference between the 

 cause which produces divergence and mutual repulsion among the atoms of a liquid on 

 becoming vapour, and that which produces a similar divergence and repulsion iu the pith- 

 balls or gold leaves of the electroscope. 



" 5th. If there be such a thing as Thermo- Electricity, we are warranted in concluding 

 that it acts in the same way, and on a similar principle, on atoms of a liquid as on those 

 of other bodies. 



" 6th. We have rational grounds for believing that explosions in steam-boilers are 

 frequently the result of the accumulated steam (present in the body of the water) being 

 suddenly released by the removal of the pressure from the denser medium of the water 

 into the lighter one of the air. ' 



" 7th. Watt's theory of steam being condensed, and reconverted into the liquid state, 

 by the direct action of cold water, is altogether erroneous. 



" 8th. Vapour or steam cannot give out its heat to water, and is but mixed, mechani- 

 cally, with it, on the true Daltonian theory." 



He next applies the theory to the explanation of the Iceland Geysers : — ■ 

 " They may be," he says, " briefly said to consist of more or less violent discharges of 

 steam and what is called boiling water from subterranean sources, each through an up- 

 right tube, which opens out above into a capacious basin. In accounting for these hot 

 springs, the existence of subterranean heat is, of course, always assumed ; but opinion 

 has been greatly divided as to the modus operandi of its application. One class of writers, 

 of whom Sir George Mackenzie may be taken as the representative, considers that sudden 

 evolutions of heat occur; that these have the effect of generating volumes of steam, 

 which accumulate in cavities with sufficient pressure to sustain the column of water in 

 the Geyser tube ; and that further sudden accessions of heat and steam produce vertical 



