The shellmounds of the environs of San Francisco Bay are almost the only witnesses of a practically unknown period in the early history of this region.[[56]] They appear to us at first investigation unintelligible, both as regards the beginning and the end of the period during which they served as human abodes. For a solution of the problem before us the most diverse kinds of investigations must be carried on, before the principal facts of this history can be clearly brought out.
Shellmounds can be found along almost all parts of the inhabited coast. In California as well as in other parts of the world they originate by the accumulation of remnants of food, especially the shells of the mollusca which are used as articles of diet. In the midst of the remnants of food cast aside by him, man clung to his place of abode, raising it more and more above the general level of the ground through the gradual accumulation of these materials. Hence these localities represent, in certain stages of human development, true but nevertheless low types of human dwelling places. The manner of procuring the essentials of life by collecting shells in itself indicates a low form of human existence. In all parts of the world, even today, people may be seen on the shore at low water gathering for food the shells uncovered by the retreating tide; and although under the changed conditions of life they raise no shellmounds, these people always belong to the lower classes of society, and lead in this manner a primitive as well as a simple life. Peoples depending for food upon collecting shells are usually not agriculturists, but fishermen, and perhaps hunters as a secondary occupation. Their implements are of the rudest kind, made of bone, stone, wood, and the like. Industries of a more highly developed kind, e.g., the dressing of ore and working it up into various implements, remained unknown to them, except in perhaps a few instances.
Thus it seems natural to connect the origin of shellmounds in general with the work of prehistoric generations, i.e., man of the stone age. The only condition necessary for their origin is, that the people who raised them lived somewhat close together and therefore possessed a certain social organization. For only in many centuries or even in tens of centuries could even large groups of men pile up such enormous quantities of kitchen debris into hills which come to form prominent features of the landscape. Though little is definitely known, the beginnings of human social organization evidently reached back into Quaternary time, just as is the case with the beginnings of human ornamentation. There is therefore no good reason why the origin of the shellmounds could not date back to Quaternary time. In this connection mention must be made of the fact that, according to Cook,[[57]] stone implements of argillite, which would consequently be attributed to the palaeolithic man, were found in a shellmound of New Jersey. The well known shellmounds of Denmark, the so-called “Kjoekkenmoeddings” (i.e., “Kitchen debris”), which first attracted the attention of scientists to the remnants left by prehistoric men, are not so old.[[58]] Nevertheless, it has been possible to prove by them that Denmark had at the time of their origin a flora considerably different from that of the present, and that the Auerhahn, too, lived there, which does not exist in Denmark today. J. Wyman, a very careful explorer of the shellmounds of New England, does not consider the Atlantic shellmounds of this continent as old as those of Denmark.[[59]] He seems to have taken this view because he met with no authentic proofs of a greater age. These were difficult to obtain. Yet he calls attention to the finding of traces of the auk, the wild turkey, and the elk in those shellmounds, i.e., animals which no longer exist in the region of shellmounds investigated by him. According to him, their disappearance took place in historic times.
In determining the age of the Emeryville mound we note first the fact that no traces of typical Quaternary animals were found in it. It is interesting to find that this mound resembles those just mentioned in regard to the finding of traces of the beaver, an animal no longer met with in this region. It was found in one of the lower strata of the mound. How far it reaches upward cannot as yet be decided, since the large number of bones taken from the upper beds have not all been examined. Since the time that remains of this animal were deposited in the lower strata of the mound, the beaver has retreated from this region, in fact from the whole of California, in a northerly direction, possibly up to Washington. When it left this region is not known. We cannot, however, be certain that this retreat may not have commenced in recent times.
Another fact of importance in fixing the age of this mound is found in the apparent change of level of the strata upon which the original layers of the mound were placed. As nearly as can be determined, the original fundament upon which the mound stands has sunk at least three feet. The base of the mound, formerly probably one foot above the usual high water level[[60]] of the bay, lies at present two feet below. If the mound with its environs had not since grown above the level of the original floor, it would be inundated completely for several hours twice a day. The length of time required for such a subsidence we can of course not determine with any exactness, as no measure of subsidence is available. In all probability it is to be taken an indication of considerable antiquity.
Further facts upon which an approximation of the age of the mound may be based are of a purely anthropological nature. Usually the early period in which man made use solely of flaked stone tools is contrasted with the later age when polished as well as chipped stone implements were used. In the very lowest stratum of the hill, almost down at the base, there were found stone implements of the well known palaeolithic turtle-back form. A pestle fragment which came from the lower stratum of the mound, though having a completely disintegrated exterior, seems to have originally been artificially rounded. A mortar fragment found low down may have originated from an implement which was formed, as is often the case, out of a common boulder. But before it broke from this object the mortar was deeply worn out, just as others that have come down to our times. Also, the deep concavity of its rims speaks for long continued wear. The next stratum (two to four feet above the base of the mound) yielded the fragment of a pestle of irregular, not rounded cross section. Here a common oblong pebble may have been used as a pestle. Besides these, the two lower strata furnished only an oval, flattened pebble, probably used as a hammer, the only one of its kind in the whole mound.
These four stone implements represent the only specimens of the two lowest strata of the mound which are not chipped. A little above these the excellently polished tool 1-8925 ([pl. 10], fig. 9) was found (in stratum VIII). This is the only one of such workmanship before the IVth stratum upwards. Therefore it is by no means impossible that rubbed or polished stone implements, excepting mortars and pestles, were unknown at the time of the origin of the lower strata, and that their use was rather limited in the succeeding strata. But the presence of mortar fragments and pestles in the lowest strata points toward a higher development of the human type than is usually expected of men who use flaked tools only.
It will have become evident from the foregoing remarks that the general zoological, geological, and anthropological facts which are available for fixing the age of the mound offer only indefinite evidence; uncertain even for an approximate dating of the time of the mound’s beginning. They do not preclude the possibility of an age numbering many centuries; neither do they prove it. Under such circumstances it seems proper to take into account some more general considerations which appear in a study of the shellmounds of the bay as a whole.
We shall probably not make too great a mistake if we estimate the number of the larger shellmounds around the Bay of San Francisco to be over 100. So many and such enormous shellmounds can not possibly have been constructed by human hands unintentionally in any small number of centuries. Furthermore, they form a link of a larger chain of similar mounds which stretch northerly along the coast and inland from Southern California to beyond Vancouver and possibly still farther; i.e., a distance of 18 degrees of latitude. The extension of such a similar manner of life over so great an area speaks of itself for the work of a great number of centuries. Even the complete development of this peculiar mode of existence, as represented in these mounds, must have taken centuries. And this is the more probably true since in those earlier stages of cultural evolution advances in the manner of living were infinitely more difficult than they were later. Under these circumstances it is only possible to assume that the origin of the shellmounds in this region represents a historical development of more than a thousand, possibly many thousand years.[[61]] If this holds good generally for the origin of shellmounds among which the one at Emeryville is, judged by its height, the character of its contents in the lower strata, and the observed geological facts, by no means the youngest, we have still to consider on the other hand the limits of the time up to which these mounds may have been inhabited.
For a long time it has been customary to consider the last as well as the first occupation of the shellmounds as belonging to the remote past. The fact that in California no shellmound is known which is now inhabited or has been inhabited in historic time would speak for this assumption. However, many instances point to habitation of the mounds in the most recent times, not only in a few places, but in different parts of the whole inhabited world. And this cannot surprise us; for we can see primitive man reach into the most recent, nay, even the present time, in various parts of the globe. Thus, as is well known, the first discoverers described the Indians of the Gulf of Mexico as men “living in houses of mats erected upon hills of oysters.”[[62]] R. Schomburgh attributes a large number of mounds made of snail shells, observed by him near the mouth of the Orinoco river, to the Warrow Indians, who are still living in that neighborhood. In the desolate coast lands of the at present dry mouths of the Ica river in Peru there are two enormous shellmounds which the writer has visited. Even now there remain large parts of the wooden huts which were left behind on these shellmounds by the last shell-eaters. Painted pot-fragments, patches of woven fibres, and all kinds of bones lie scattered about. It would be an easy matter to show that the last inhabitants of the hill exhibited the later cultural conditions which prevailed during the time of the Incas in the valleys of Pisco and Ica, about 1460 A.D.