ox THE COAST OF MAINE. 325 



land we have distinct evidence to show that the depression at the close of the glacial period 

 amounted to over one hundred and fifty feet, while at Boston there is good reason to 

 believe that it did not exceed half this amount. Along Avith the evidences of greater subsi- 

 dence there are other facts which go to show a longer continuance of the depression. The 

 area of the brick clays and other deposits which show the gradual silting action which must 

 have taken palace when the sea was separating the mud from the gravels of the drift is 

 much greater in this section than in Massachusetts. Following up the valley of the I'iver 

 towards Lewiston, these clays and stratified sands are seen in an abundant development. 

 All along the section from Portland northward, sections answering in general character to 

 that shown in Fig. 1, abound. These sections unquestionably indicate something like the 

 following histoiy. The massive drift, the 



remains of which are still seen in the 



lower part of the section, retaining the l ut^^^zttz 



shape in which it was dropped at the '^^ zr^ i n . — g 



melting of the ice sheet, has first been 'Z^T-Znir.^^ ~iz 



worn away by the action of the marine - „- — ^- ^ ^ ^ C'p^^r y 



currents, and afterwards covered by the --— ->^^ r^i °'^^^J2? O'^r^Q _ 

 finer materials torn away from some — 'c? "^ <j c> •o c^ 3<^ O Q C^"^~^ 

 other part of the drift sheet. The im- Pm, j. 



lavs. 



perfect stratification of the upper part of ''• Stratified cla 



,, ,. , ,1 •! ,1 J ;i ^- Maj?ive drill with antjular boulders quite unstratified. 



these sections suggests the idea that the 



force which swejDt the materials to their present place was of paroxysmal violence. I have 

 treated the question of the origin of these table drifts in a report on the surface geology of 

 the region about Massachusetts Bay, and shall not therefore repeat the matter here ; the 

 conclusion to which we seemed compelled was that the elevation of the land was likely 

 enough of great suddenness, after the fashion of observed changes on the South American 

 coast, and that to the sweep of the receding sea, aided, it may be, by a succession of earth- 

 quake ocean waves, we owe the rapid accumulation of these curious table drifts. The 

 materials swept away from the coast of South America by the great waves which have 

 swept against the shore during the last one hundred years must he in a manner very sun- 

 Uar to the masses we have in these rudely stratified drifts. 



In crossing from the vallej' of the Kenuebeck to that of the Penoljscot, we rise at the 

 level of from two to three hundred feet into the region of the ordinary upland drift, such 

 as covers a large part of Massachusetts. This depo.sit does not, in any regard, diifer from 

 that foimd further south, unless it may be in the greater size of the fragments which some- 

 times are found in the mass. I am tempted to believe, from the great variety of the 

 materials found together, that on the whole the transportation from great distances is much 

 more common here than in Massachusetts. 



On the Penobscot Bay the quantity of drift material, and its disposition, difiers somewhat 

 from what we find on the Kenuebeck. The mass of the detrital matter seems greater, and 

 the amount of silt beds much less than near Portland. At Belflist, where the drift is seen 

 to considerable advantage, the following points are observed. The 2)i'iuci2)al channel of the 

 bay, and the minor streams which fall into it, are both quite free from evidences of the 

 local secondary glaciatiou, such as we found in the vallejs of the streams near Boston. 

 The reason for this is easily found without supposing that the secondaiy glaciers were want- 



MEJIOIKS BOST. SOO. KAT. HIST. VOL. II. 



