THE VOYAGE OF H.M.S. CHALLENGER. 
-xxviii 
Thomson, Murray, and Buchanan,’ dealing with the nature and origin of the marine 
deposits procured in the various sounding and dredging operations. 
Since the return of the Challenger Expedition very many samples of marine deposits 
have been collected from nearly all regions of the ocean basins by the surveying vessels 
of the Briti.sh Navy, by the telegraph ships belonging to the India-rubber, Gutta-percha, 
and Telegraph Works Company, and to the Telegraph Construction and Maintenance 
Company, and by Norwegian, Italian, French, German, and American Expeditions. The 
great majority of these sainjdes have passed thi'ough our hands, and have, along with the 
Challenger collections, formed the material for our investigations. 
In the jiresent work we have endeavoured to point out the composition and mode of 
formation of marine deposits in general, as well as the distribution of the different types 
over the door of the ocean. In many cases we have indicated the resemblances and 
differences between these deposits and certain geological formations, but we have not 
discus.sed in detail the wider geological bearings of the results arrived at from these 
re.searche.s. If it be remembered that, previous to the recent scientific explorations of the 
great ocean basins, we passessed no positive knowledge concerning the organic and minera- 
logical components of the deposits now forming over more than one-half of the earth’s 
surface, the im[)ortance of the Challenger’s discoveries, as to the nature of the sea-bed, 
on all inquiries regarding the past history of our globe will be readily appreciated. « 
'I'he large amount of material at our command has enabled us to divide marine 
dcjKjsits into two great categories — Terrigenous Deposits and Pelagic Deposits. 
The Terrigenous Deposits include those now forming along the littoral zone, in 
shallow water, and on the continental slopes beyond the 100-fathom line. They are, 
for the most part, composed of materials washed down from emerged land, the various 
comjKjnents exhibit abundant traces of mechanical action, and the accumulation is 
relatively rapid. Among these terrigenous deposits it is possible to recognise an accumu- 
lation of materials analogous to those forming certain schistose rocks, shales, marls, 
grecn.sands, chalks,* j)hosphatic and other limestones,^ volcanic grits, quartzites, and sand- 
Htonc.H of gcologiail formations.^ 
* See /'roe. Hoy. Soc., vol. xxiv., 18Tfi 
* The DAture of the niincnil particlcH nml pchhles of the chalk, the evidences of mechanical action, the variability 
of the n*idue of the chalk, the chemical aiialysiH, the character of tlie orj^anic remains, and the position of the Cretaceous 
*=■*, ell point to the white chalk l>ein({ formed near shore, and not in the abysmal rej'ions of a deep ocean like a typical 
(>lobi(;erina 0»zc (itee L. Cayenx, “ I>a Craie du Nonl de la France et la Hone a Globigerines,” Ann. Son. g(fol. du Nord, 
tom. xix. pp. 95-102, 1891, and other j«p<*ni by the same author). The same remarks are ai)j)licable to certain calcareous 
and liliceoux rock* of the Alp (sec F. Wuhner, “ Aus <ler Urzeit unserer Kalkalpen,” Zeitnehr. d. Deutschen und Oeslerr. 
AljimtyreinA, B<1. xxii. pp. H7-124, 1H91). 
* In some tiTri>p’nou* depwita there appears to lie distinct evidence of the coiiimencement of dolomitisation. 
‘ The area covere«l by tiTri({cnous depjaiU (from the const line seaward to an average disPince of about 200 miles, 
and down to an avemgi' depth of alK>ut two miles) has lx:en calle«l by Mr. Murray the Transitional Aren. It covers 
about one-seventh, while the land stirfacir occupies two-sevenths, and tlie plagic deposits four-sevenths of the earth’s 
surface. Mr. Murray holds that all the marine stratifie<l rocks of the continents have in past times been laid down in 
regions corresponding to the Transitional Area. 
