"No tools have yet been met with in any of the gravels occurring at the higher levels of the valley of the Seine; but no importance can be attached to this negative fact, as so little search has yet been made for them"

This quote by Charles Lyell is describing the absence of tools discovered in the gravels of the Seine Valley. Lyell is recommending that the absence of tools is not considerable, as there has not been a comprehensive search for them. He is indicating that if a more comprehensive search was performed, tools might be found. Lyell is likewise recommending that the lack of tools discovered in the gravels of the Seine Valley is not a sign of the existence or lack of human activity in the location. He is recommending that more research is needed to figure out if humans existed in the location. Lyell's quote is a suggestion that the lack of evidence is not always evidence of lack. It is necessary to conduct comprehensive research before making any conclusions.