20 LOWER OOLITIC ROCKS OF ENGLAND: 
The association of algous growth with the deposition of travertine, in 
connection with the Warm mineral waters of Carlsbad, has been shown by 
Dr. F. Cohn, and the subject has been discussed at some length by Mr. 
W. H. Weed.* 
The connection between calcareous algae and oolitic granules has been 
suggested by several authorities. f Such algje often enter largely into 
the composition of recent Coral-rock. 
The oolitic granules in our Jurassic rocks would appear to have been 
in most, if not in all cases, of inorganic origin ; but the chemical de- 
position of calcareous matter may have been influenced by the presence 
of algous growths, as they abstract carbonic acid from the water. 
The modern formation of " oolitic sand " on the shores of Lake Bomio- 
ville, in Utah, has been noticed by Mr. G. K. Gilbert. It constitutes the 
materials of a beach and is drifted shoreward in dunes. In one locality 
its formation is near the month of a stream, and in another it is connected 
with hot calcareous springs.]; Here again we have the formation of 
oolitic granules in waters subject to commotion. Mr. I. 0. Ruesell states 
that oolite is now forming on the borders of Pyramid Lake, Lahontan, 
Nevada : it occurs near warm springs, and some of the granules are an 
inch in diameter. The nuclei are sand-particles, &c. 
Mr. C. Reid informs me that oolitic concretions, that exceed the size of 
hazel-nuts, have been formed by a calcareous spring that issues from 
the Oligocene limestone at Totland Bay, in the Isle of Wight.|| 
It is interesting to note that the soundings marked over the sea- 
bed in the northern area of the Great Barrier reefs, show in different 
places coral snnd, coral fragments, mud, mud smd sand, and sand.^f 
Such varying accumulations are taking place in some places near 
the reefs ; and in others near the mainland where no reefs occur 
and where river borne sediments may be distributed. While such 
facts indicate the variable nature of the sea-bed, the general con- 
ditions of a Coral-region may help to account for some of the local 
successions of clay, sand, and shallow-water limestone to which 
attention has been drawn. Dana has given particulars of borings 
in Coral -regions that show alternations of sand, coral-rock, and 
clay to depths of 700 and 1,000 feet,** 
Clays form what has been termed the " normal " (that is the 
more prevalent) type of sediment during the Jurassic period ;ft and 
they were deposited over certain areas until gradunlly the increase 
of sediment, or changes in physical conditions affecting currents, 
brought about the deposition of sands. Finally the freedom from 
muddy sediments furnished conditions favourable to the growth of 
Corals, and the old lands were bordered in places by reefs. Such 
reefs, whether Fringing or Barrier reefs, afford protection to the 
land, as pointed out by Jukes, so that the rarity or absence, in 
deposits associated with them, of detrital material from the land 
is accounted for. Thus fine calcareous sediment may be deposited 
* Ninth Ann. Rep. U.S. Geol. Survey, 1889, pp. 631, 642, &c. 
t H. G. Sceley, Rep. Brit. Assoc. for 1888 (1889), p. 675. Dr. A. Rothpletz, 
Botanisches Cer.tralblatt, No. 35, 1892 (Amcr. Geol., vol. x. p. 279). 
J Lake Bonneville, Monogr. U.S. Geol. Survey, vol. i. p. 169. 
Monogr. U. S. Geol. Survey, vol. xi. pp. 61, 168. 
f| Geol. I. of Wight (Geol. Survey), ed. 2, p. 2?9. 
^1 Chart attached to Jukes' Voyage of the "Fly," vol. i. ; see also W. Saville- 
Kwnt, Great Barrier Reef of Australia, 1893. 
** Amor. Journ. Science, ser. 3. vol. xxxvii. p. 96. 
f1 See J. V. Blake, Rep. Brit. Assoc. for 1879, p. 335 } and Nature, 1679, p. 470. 
