January 10, 1908] 



SCIENCE 



73 



of beds, but more probably tbe deposition of 

 tlie Altamaha resulted in the intermixing of 

 beds of similar material, thus obliterating any 

 sharp line of contact between the two, and the 

 apparent continuity of deposition may be thus 

 accounted for. Likewise, at Attapulgus, in 

 Decatur County, red sands and green clay 

 overlie without noticeable unconformity a 

 fuller's-earth deposit, which is regarded as 

 being the equivalent' of the Alum Bluff beds. 

 An excellent vertical section, showing the 

 relation of the Altamaha to Miocene strata, 

 is exposed in the bluff of the Altamaha E.iver 

 at Doctortown, where thirty feet of stratified 

 Altamaha clay and sand overlie a fossiliferous 

 bed containing Miocene pectens. The fossil- 

 iferous bed here is four feet thick and is com- 

 posed of bluish-gray sand full of large pectens 

 and a calcareous sandy layer one foot thick, 

 full of small bivalves and comminuted shells. 

 The section of the bluff is: 



Feet 



1. Yellow and mottled argillaceous sand 10 



2. White and yellow cross bedded sand con- 



taining thin layers of small pebbles .... 10 



3. Red and yellow stratified sand, containing 



thin clay laminjc or leaves 10 



4. Calcareous fossil sand 1 



5. Bluish sand, containing pectens 3 



6. Bluish sand clay 7 



No. 1 of this section has the typical mot- 

 tling of the Altamaha sand and brown iron 

 oxide accretions are found at the surface as 

 elsewhere over the Altamaha region. The 

 above section is of considerable interest be- 

 cause of the light that it throws on the age 

 of the upper thirty feet of strata. The bluff 

 is referred to by Dal? as being Altamaha grit 

 and is described by McGee' as Lafayette. A 

 section identical with the one given above 

 occurs at Linders Bluff, three miles above 

 Doctortown, and similar sections are found 

 in the bluffs of the Altamaha River several 

 miles below Doctortown — the upper and lower 

 Sancivilla bluffs. No fossils, however, were 

 observed at the Sancivilla bluffs, except bits 

 of lignitized plant remains. 



'T. W. Vaughan, Bull. No. 213, p. 392. 



' Bull. No. 84, U. S. G. S. 



' U. S. G. S., 12th Ann., Pt. I., p. 484. 



The Altamaha has not been identified with 

 certainty lying in contact with strata bearing 

 Pliocene fauna, but there is strong probability 

 that it does overlie such strata. A marl bed 

 overlain by clayey sand outcrops on the Satilla 

 River six miles below Atkinson, from which 

 fossils were collected by Mr. S. W. McOallie 

 and identified by Mr. T. H. Aldrich, as be- 

 ing Pliocene. The Altamaha is exposed at 

 Waynesville, a few miles east of Atkinson, 

 and undoubtedly overlies the above-mentioned 

 marl beds on the Satilla River. Also, marine 

 shells and vertebrate remains brought up by 

 recent dredgings at Brunswick further suggest 

 the probability of Pliocene fossil beds near the 

 coast. 



Overlying the Altamaha formation uncon- 

 formably there is everywhere a thin mantle or 

 superficial layer of loose sand of Pleistocene 

 age. This sand is a light gray or brown in 

 color, shows no stratification, is free from clay, 

 and is always easily distinguished from the 

 Altamaha. It varies in thickness from to 

 50 or 60 feet, and the average thickness is not 

 more than 10 feet. This sand presents a 

 remarkable uniformity in color and texture 

 throughout the whole coastal plain, from the 

 sand hills of the fall line to the Atlantic coast. 



Summing up the known facts concerning 

 the Altamaha formation, the writer is inclined 

 to regard it as being late Pliocene in age. The 

 formation itself contains no fossil evidence 

 which will aid in determining its position, 

 being devoid of all fossil remains except a few 

 bits of wood; and the conclusion concerning 

 its age is reached from the knowledge that it 

 overlies Miocene and Pliocene strata and is 

 older than the coastal Columbia sand, which is 

 of Pleistocene age. The correlation of the 

 numerous exposures of the Altamaha has been 

 determined by stratigraphical continuity, 

 homogeneity and physiographic features. Be- 

 ginning with an outcrop of typical Altamaha 

 in the northern part of the Altamaha region, 

 it was traced by examination of exposures at 

 short intervals to the Atlantic coast and to 

 Florida. In Georgia, at least, it is believed 

 that it is identical with the formation which 

 McGee considered Lafayette. In his study of 

 the Lafayette in Georgia, in the Twelfth An- 



